AS VIEWED BY MARINER 9
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NATIONAL AERONAUTICS AND SPACE ADMINISTR ATtniM
LIBRAR.Y OF
WE LLESLEY COLLEGE
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NASA SP-329
AS VIEWED BY MARINER 9
A Pictorial Presentation by
the Mariner 9 Television Team
and the Planetology Program
Principal Investigators
Revised
Scientific and Technical Information Office
NATIONAL AERONAUTICS AND SPACE
1976
ADMINISTRATION
Washington, D.C.
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Library of Congress Catalog Card No. 73-6001 'i!
For sale by the Superinlenileiit of Docmiienls
U.S. Government Printing Office. Wa.shintiton, D.C. 20402
Priee $6.30/Stoek No. 0.'?:< - 000- 0064.S
■t! US- GOVERNMENT PRINTING OFFICE 1976 O- 205-853
Foreword
In the annals of space exploration, a very particular
place must be reserved for a 546-kg metal object that,
tumbling and silent now, is encircling an alien planet
hundreds of millions of kilometers from its native Earth.
It will remain, we think, in this remote orbit for at least
half a century — unless perhaps some earthbound caravel
of the far future picks it up for return to a place of
honor in the land of its origin. This metal object is the
Mariner 9 spacecraft, a singularly responsive mechanism
at the end of an exiguous electromagnetic link that per-
formed one of the most remarkable missions in the his-
tory of planetary exploration.
From the beginning — before, in fact — it was an ex-
ceptional mission. A twin spacecraft, programmed to do
half the mapping and scientific reconnaissance of the
planet Mars, died at birth, a victim of launch-vehicle
failure. The Mariner team, working coolly under difficult
constraints, rebuilt the flight plan and orbit of Mariner 9
to accomplish as many as possible of the scientific objec-
tives of both missions. Then, after 157 days of inter-
planetary flight, the spacecraft arrived at Mars and suc-
cessfully entered orbit — becoming the first human artifact
ever to orbit another planet — only to encounter a planet-
wide dust storm that was veiling the surface of Mars.
Although this forced postponement of the mapping mis-
sion for many weeks, it did provide an excellent opportu-
nity to study the storm beneath. After the storm abated,
Mariner 9 set about a mapping and scientific reconnais-
sance of exceptional quality and value. It photographed
virtually the whole surface of the planet, sent more than
7000 images back to Earth, and relayed a total of more
than 30 billion bits of information, an amount equivalent
to 36 times the entire text of the Encyclopaedia Britan-
nica. This is incomparably more than had been received
from all earlier planetarv missions together. The pictures
in this volume, which is but one of many scientific re-
ports to derive from the mission, provide in their view
of canyons and giant crevasses, craters and volcanoes, a
new and exciting understanding of the red planet.
James C. Fletcher. Administrator
National Aeronautics and Space Administration
Preface
Mariner 9 was launched from Kennedy Space Center
on May 30. 1971. A midcourse maneuver on June 5
placed its aiming point so close to Mars that no addi-
tional course correction was necessary. The spacecraft
was successfully inserted into Mars orbit on November 14
at 00:15:29 GMT, becoming the first manmade object to
orbit another planet.
Initiated in 1968, the Mariner Mars 1971 Program
had called for two spacecraft to orbit Mars during the
1971 opportunity, one in a high inclination orbit and the
other in a low inclination orbit. After Mariner o was lost
during launch on May 9. the operational strategy was
changed to an intermediate inclination orbit to achieve
maximum scientific return from a single orbiter. The
objective of the mission was to explore Mars from orbit
for a period of time sufficient to observe a large fraction
of the surface and to examine selected areas for dynamic
changes. Imagery of the surface was to be obtained as
well as significant data on the atmosphere and surface
characteristics.
Eleven Principal Investigators were concerned with
the six experiments carried by Mariner 9:
Television — H. Masursky (team leader). U.S. Geological
Survey, Flagstaff; G. Briggs, Jet Propulsion Labora-
tory; G. De Vaucouleurs. University of Texas; J. Led-
erberg. Stanford University: B. Smith. New Mexico
State University.
Ultraviolet spectroscopy — C. Barth, University of Colo-
rado.
Infrared spectroscopy — R. Hanel, NASA Goddard Space
Flight Center.
Infrared radiometry — G. Neugebauer. California Institute
of Technology.
S-band occultation — A. Kliore, Jet Propulsion Laboratory.
Celestial mechanics — J. Lorell (team leader), Jet Propul-
sion Laboratory; I. Shapiro. Massachusetts Institute of
Technology.
The spacecraft was approaching Mars, when tele-
scopes on Earth revealed that a planetwide dust storm had
broken out and was totallv obscuring its surface. From
November to mid-December only faint markings appeared
on the surface of Mars and sometimes a diffuse feature
with a series of billowing dust waves on its lee side. The
last picture taken before orbital insertion had shown four
curious dark spots aligned in a T-shaped pattern, and it
was theorized that thev might be high-standing parts of
an otherwise obscured planet. This area was monitored
repeatedly during the course of the storm, and as succes-
sive pictures showed more and more detail it became
clear to the science team that these were the summit areas
of enormous volcanoes protruding through the top of the
dust cloud. By the end of December it appeared that the
dust storm was diminishing and that the planetary map-
ping sequences could soon begin.
From January 1972 onward, every week was punc-
tuated by new and startling discoveries. First there were
the enormous volcanoes standing as much as 15 miles
above the average surface, each one about the size of
Arizona. Then, totally unanticipated, immense canyons
appeared, including a great equatorial chasm more than
ten times the size of the U.S. Grand Canyon. The canyons
proved to have eroded walls, and in addition numerous
dendritic tributaries extended back from the canyon walls,
suggesting that water erosion may have played a role in
sculpturing the surface of Mars some time in its past. Yet
it was known from previous flyby missions that atmos-
pheric and surface temperature conditions are such as to
prevent liquid water from existing in adequate quantity at
the present time. For this reason the science team was
astounded by the apparent evidences of erosion, and then
by the discovery of non-canyon-related sinuous channels
that had all the earmarks of dry river valleys. Eroded
cliffs appeared, as well as wind-erosion features and large
dune masses. It is difficult to convey the sense of high
excitement that pervaded the scientific investigators as
the newly perceived character of our sister planet began
to unfold.
Soon it became apparent that almost all generaliza-
tions about Mars derived from Mariners 4, 6, and 7
would have to be modified or abandoned. The partici-
pants in earlier flyby missions had been victims of an
unfortunate happenstance of timing. Each earlier space-
craft ( except in part for Mariner 7. which had returned
startling pictures of the south polar regions) had chanced
to fly by the most lunar-like parts of the surface, return-
ing pictures of what we now believe to be primitive,
cratered areas. Given a difference of as little as six hours
in arrival times of any of these earlier spacecraft (each of
which had spent many months in transit), an entirely
different view of Mars would have resulted. It was almost
as if spacecraft from some other civilization had flown by
Earth and chanced to return pictures only of its oceans.
Mars moved behind the Sun in early August 1972,
and the spacecraft could no longer be commanded from
Earth. At this point in the mission nearly all the planet
had been mapped with the low resolution camera, and
about 2 percent of its surface covered by the high resolu-
tion camera, specially targeted over points of high scien-
tific interest. In addition, the waning of the south polar
cap had been examined in detail, and the layered and
pitted deposits in these regions extensively pictured. At an
altitude of 1650 km the resolution of the TV camera sys-
tem was about 1 km for the low resolution camera and
about 100 m for the high resolution camera.
When Mars came out from behind the solar corona
on October 12, so that scientific operations with the
orbiter could be resumed, mapping coverage of the north-
ern latitudes was completed and the northern polar re-
gions examined in detail. After a lifetime in space of
516 days, the Mariner 9 spacecraft ran out of attitude-
control gas and tumbled out of control on October 27,
1972, almost one year after it had been inserted into Mars
orbit. — J. F. McCauley, H. F. Hipsher. and R. H. Stein-
bacher.
Contributors
J. W. Allingham
U.S. Geological Survey
Washington
G. A. Briggs
Jet Propulsion Laboratory
M. H. Carr
U.S. Geological Survey
Menlo Park
S. E. Dwornik
NASA Headquarters
W. E. Elston
University of New Mexico
J. C. Fletcher
NASA Headquarters
P. L. Fox
Cornell University
D. E. Gault
NASA Ames Research Center
M. Gipson, Jr.
Virginia State College
R. Greeley
NASA Ames Research Center
M. J. Grolier
U.S. Geological Survey
Washington
N. W. Hinners
NASA Headquarters
H. F. Hipsher
NASA Headquarters
H. E. Holt
U.S. Geological Survey
Flagstaff
J. H. Howard HI
University of Georgia
K. A. Howard
U.S. Geological Survey
Menlo Park
E. A. King, Jr.
University of Houston
J. S. King
State University of New York
Buffalo
T. J. Kreidler
U.S. Geological Survey
Flagstaff
C. B. Leovy
University of Washington
J. F. McCauIey
U.S. Geological Survey
Flagstaff
D. T. McClelland
Hamilton College
T. R. McGetchin
Massachusetts Institute of Technology
G. E. McGill
University of Massachusetts
J. D. Murphy
State University of New York
Buffalo
H. Masursky
U.S. Geological Survey
Flagstaff
E. C. Morris
U.S. Geological Survey
Flagstaff
T. A. Mutch
Brown University
J. E. Peterson
University of Colorado
J. B. Pollack
NASA Ames Research Center
D. B. Potter
Hamilton College
L. Quam
Stanford University
C. Sagan
Cornell University
R. S. Saunders
Jet Propulsion Laboratory
D. H. Scott
U.S. Geological Survey
Flagstaff
R. P. Sharp
California Institute of Technology
E. M. Shoemaker
California Institute of Technology
B. A. Smith
New Mexico State University
L. A. Soderblom
U.S. Geological Survey
Flagstaff
R. H. Steinbacher
Jet Propulsion Laboratory
J. Veverka
Cornell University
D. E. Wilhelms
U.S. Geological Survey
Menlo Park
J. F. Woodruff
University of Georgia
Contents
Page
1
1
Introduction
5
2
Giant Volcanoes of Mars
27
3
Mysterious Canyons
41
4
Channels
57
5
Fractures and Faults
71
6
Escarpments
83
7
Fretted and Chaotic Terrains
91
8
Craters
101
9
Wind-Shaped Features
113
10
Changing Features
125
11
Extensive Plains
133
12
Polar Regions
149
13
Clouds of Mars
163
14
Natural Satellites
169
15
Martian Enigmas
185
16
Similarities; Mars, Earth, and Moon
221
Availability of Photographic Prints
223
Shaded Relief Map of Mars
1
Introduction
Although the dust storm delayed the start of system-
atic mapping, it afforded an unparalleled opportunity to
examine its effects on the surface and atmosphere of Mars.
Pictures of the limb were taken showing that dust reached
the enormous elevation of about 70 km (43 mi.). Grad-
ually features emerged through the haze. At first only the
dimly shining south polar cap and four dark spots could
be seen. One of the dark spots had been noted during the
dust storms of 1924' and 1956 by astronomers. Lnder nor-
mal conditions this feature appears as a bright white spot,
Olympus Mons. The other three spots lay in the area
where periodic brightenings called the "W-cloud" have
often appeared. As the storm gradually subsided and the
atmosphere cleared, the four spots turned out to be high
mountains with craters at their summits. Olympus Mons
appeared as an immense shield volcano 24 km high with
long finger-shaped lava flows on its flanks — the largest
volcanic pile ever photographed. Later a great plateau
became visible, sloping to the east from the volcanoes.
On it appeared a bright stripe that later turned out to be
a great equatorial chasm.
The more than 7300 pictures acquired from Mariner
9 indicate that Mars is more varied and dynamic than
previously inferred. Although impact craters are common,
only a few small craters show continuous ejecta blankets
and well developed rays. Most small craters, however,
exhibit degraded, irregular ejecta blankets. About half
the surface consists of ancient cratered terrain surround-
ing large impact basins. The largest circular feature. Hel-
las Planitia, is almost twice the size of the largest basin
on the Moon. Mare Imbrium. Argyre Planitia is ringed
by radially and concentrically textured mountainous ter-
rain, similar to the lunar multi-ringed impact basins such
as Imbrium and Orientale. The remainder of the surface
is covered by younger volcanic rocks and volcanoes. These
rise as much as 25 km above the mean level of extensive
lava plains deposits, some of which contain windblown
or possibly fluviatile deposits that are sedimentary in
origin. The single volcanic edifice of Olympus Mons,
which rises high above the floor of Amazonis Planitia. is
almost three times the width and height of the largest of
the Hawaiian volcanoes. Mauna Loa. Three other large
volcanoes lie along the Tharsis ridge. The volcanoes with
summit calderas have fresh flows on their slopes and ap-
pear to be relatively young. These volcanic vents provide
a plausible source for much of the carbon dioxide and
water in the atmosphere. The great equatorial chasm or
canyon svstem. Valles Marineris, comparable in size to
the East African Rift Vallev svstem, is as much as 6 km
deep and greater than 5000 km long, the distance from
Los Angeles to New York City. It terminates in a com-
plexly faulted plateau to the w'est, and in large patches of
chaotic terrain to the east.
Emerging from the northern plateau lands, a com-
plex array of broad sinuous channels descends into a
regionally depressed area. Large fluvial channels begin in
this chaotic terrain — possibly from episodic melting of
permafrost — and seem to flow northw ard into the Chryse
Planitia lowland. The channels merge on the border of
the flat, low Chryse area: here the channel floors show
multiple braided features and streamlined islands. It has
been proposed that the collapse of these rocks and forma-
tion of large-scale landslides may be caused by melting
of permafrost.
Other large sinuous channels with many tributaries
have no obvious sources. Small dendritic channel net-
works abound in the equatorial regions and imply pos-
sible rainfall. Many of the basin floors are underlain by
lava flows having lobate fronts, and are inferred to be
basaltic from the form of the flows, ridges, and broad,
low mare-type domes that characterize their surface.
The polar regions are covered by glacio-eolian lay-
ered rocks that appear to be still forming under the pres-
ent climatic regime. Older massive deposits are being
eroded, pitted, and etched into troughs around the mar-
gins of the poles. Young layered deposits resembling thin
laminae overlie the etch-pitted unit. The individual thin
layers appear to be cyclical deposits. High velocity wind
is stripping the surface and forming deflation hollows. A
mantle of ^vindblo\vn debris, presumably derived from
these circumpolar zones, thins toward the equator. These
deposits smoothly blanket a subdued cratered terrain and
partially fill its craters. The south and north polar regions
have a])parently acted as sediment or dust traps through-
out much of Mars history.
Both eolian erosional features such as yardangs
(wind eroded ridges I and depositional features such as
dunes have been identified in the equatorial region. One
dune field, about 130 km long, lies on the floor of a
crater. Wind erosional and depositional processes are ac-
tive, as seen by numerous changes in the albedo patterns
that were monitored after the clearing of the planetwide
dust storm. Redistribution of deposits of silt and clay
particles reveals dark, irregular markings and light and
dark tails emanating from topographic obstacles. The
light tails appear to be wind-deposited material: the dark
tails appear to be mostly wind-scoured zones. Throughout
the mission clouds of various patterns composed of CO2
ice crystals, water ice crystals, and local wind raised dust
clouds were observed.
The temperature measurements and cloud patterns
led to interpretations of the planetwide atmospheric cir-
culation pattern, which in turn could be compared with
the bright and dark surface markings that also indicate
wind directions. Changes in the surface patterns were
monitored on a periodic basis. During this time the dark
markings that had been, observed from Earth telescopes
for more than a hundred years gradually reappeared
after having been obscured by the storm deposits.
The retreats of both the north and south polar ice
caps were observed closely. The carbon dioxide and pos-
sibly some water ice retreated by sublimation, revealing
layered deposits formed by glacial-like processes, and a
belt of etched pitted terrain surrounding the polar ice-cap
region. The hollows may be formed by wind erosion, for
the winds at the margins of the polar caps have a very
high velocity on Mars, as they do on Earth in Antarctica
and near the Greenland ice cap.
The spacecraft ceased functioning when it ran out of
attitude-control gas after .349 days in orbital operation.
It succeeded its design lifetime by almost a factor of four. Mars in 1975-76 that involve landing spacecraft on the
and its observations exceeded all science goals. Mariner 9 surface of Mars to search for life. — H. Masursky and
data will greatly assist planning for the Viking flights to B. A. Smith
2
Giant Volcanoes of Mars
Recognition of prominent volcanic features on Mars
was one of the first and most significant results of the
flight of Mariner 9. During the fully developed dust storm.
the only surface features clearly visible outside the polar
areas were four dark spots in the Amazonis-Tharsis re-
gion. As the atmosphere cleared, those spots were seen
to be the central calderas of four enormous shield vol-
canoes. Subsequent photography of other parts of the
planet revealed more volcanic features, indicating that
volcanism played a major role in the evolution of Mars.
Past volcanic activity includes formation of extensive
plains units, and building of the tremendous shield vol-
canoes and numerous smaller dome-like structures.
Most of the volcanic features except the plains are
in the regions of high elevation. The three shield volca-
noes, the Tharsis Monies, lie on a broad ridge which is
3 to 5 km above the mean level of the martian surface.
Olympus Mons. the largest of the volcanic shields, lies
on the western flank of this ridge. Olympus is 500 km
wide and rises 29 km above the surrounding plain. The
Tharsis Monies, Ascraeus. Pavonis, and Arsia Mons are
each about 400 km across and. although smaller than
Olympus Mons, may reach the same elevation above the
mean level of Mars because of their location on a ridge.
In comparison, the largest volcano on Earth. Mauna Loa
in Hawaii, is approximately 200 km wide and rises about
9 km above the sea floor.
All shield volcanoes have roughly circular outlines
and central summit depressions. Arsia Mons, Pavonis
Mons. and an Elysium shield. Albor Tholus, have simple
craters at their summits. Olympus Mons and Ascraeus
Mons have complex craters as a result of successive col-
lapses around different centers. Other volcanoes, differing
from shield volcanoes in that they are smaller and simple,
are properly termed domes or tholi.
The shields and domes are the most spectacular
aspects of martian volcanism, but the plains on Mars
may be volumetrically more significant. High resolution
pictures of the plains commonly show long, low, lobate
scarps (possible flow fronts) that strongly resemble fea-
tures in Mare Imbrium on the Moon. By analogy with the
lunar maria and terrestrial flow fronts, the plains are
probably largely volcanic in origin.
In many places the cratered surface appears to be
partly or wholly covered by younger plains-forming mate-
rials. In some areas only the small craters are buried, in
others even the largest craters are buried entirely or show
only subdued impressions. Such effects could result from
eolian deposition, but volcanic activity also appears to
have been widespread and products of this activity also
may cover part of the cratered surface. Both volcanic
plains and circular constructional features are found
within the densely cratered province. Thus, although the
most spectacular volcanic features occur in sparsely
cratered regions, the entire planet may have been affected
by volcanism. — M. H. Carr
^^^!^'
(20°N, 135°W: MTVS 4133-96)
Long lava flows (above left) are visible in this photograph of the northwest flank of
Olympus Mons (resolution, about 100 m). Many show natural levees such as occur
along the margins of many terrestrial lava flows. The most prominent ridge has a
channel ( arrow I 250 m wide along 36 km of its crest that is inferred to be a lava chan-
nel. Lava flows of this form are characteristic of basaltic eruptions in the Hawaiian
and Galapagos Islands on Earth. — H. Masursky
(18°N, 133°W; MTVS 4265-52)
The central caldera (above right) on Olympus Mons shows a structure of intersecting
collapse depressions and concentric fractures. The inward collapse of the caldera
floor is evident from the terrace pattern that steps toward the caldera center, a pattern
similar to terrestrial volcanic calderas. The smaller, youngest, collapse pit (top center) ,
is about 30 km across. — H. Masursky
(18°N, 133°W)
Photomosaic of Olympus Mons (facing page), the largest of the Mars volcanic moun-
tains. The volcanic structure is 500 km across and about 29 km high, with a complex
summit caldera about 70 km across. These dimensions make it the largest volcanic
structure known. It is much larger than the island of Hawaii, which (on the ocean
floor ) at 200 km across and 9 km high is the largest volcanic pile on the Earth. The
scarp around the base of Olympus Mons stands 1 to 4 km high and may have been
produced by wind erosion. Originally the volcanic pile probably graded smoothly into
the surrounding plain. — H. Masursky
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(1°N, 113°W; MTVS 4267-44) ,
The central crater and ring structure of Pavonis Mons are shown in this oblique view
(above). The smooth crater-free floor and talus on the walls of the summit pit, and a
series of collapse terraces at the sides, are clearly visible. Radial ridges, similar to lunar
mare ridges, connect the central pit to the ring structure of grabens and horst ridges.
The dark patches formed during the mission and were almost certainly produced by
eolian processes. — M. H. Carr
(1°N, 112°W; IPL 1699/125324)
The shield volcano at Pavonis Mons (left) is about 400 km across and rises more than
20 km above the surrounding plains. Concentric graben occur on the flanks of the
shield and in the surrounding plains. The caldera consists of a single large circular
depression. 55 km in diameter. — :M. H. Carr
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(1°N. 113°W; MTVS 4142-93)
Part of the summit caldera of Pavonis Mons is shown here. The caldera-wall fluting is
probably caused by debris avalanches cutting large grooves down the steep slope.
Talus debris may overlie narrow terrace benches. The smooth caldera floor, which
abruptly meets the steep walls, may represent the surface of a former lava lake. Well-
defined impact craters with sharp rims ranging from 1/2 to 2 km are visible on the
flanks of the volcano. — M. H. Carr
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(1°N, 113°W; IPL 7388/011543)
The ridges around Pavonis Mons are here shown enlarged, revealing their similarity to
lunar maria ridges. They are inferred to be extrusions of lava along a complex fracture
system extending more than 30 km down the flanks of the shield volcano. The dark
patches shown in a previous picture have not yet developed. — M. H. Carr
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(13°N, 89°W; MTVS 4189-72)
Tharis Tholus (above). 170 km in diameter, is one of several similar volcanic domes
near the Tharsis Montes. The central crater is multiple, has a flat floor and steep walls
with several terraces. The flanks of the dome appear to have been faulted ( upper right) .
Domes may form instead of the larger and more gentle shield structures when only
small volumes of lava are available. Alternativelv. they may indicate more viscous and
possibly more siliceous lava. — M. H. Carr
(13°N, 106° W; MTVS 4184^84)
Ascraeus Mons (left), the northernmost large volcano along the crest of Tharis ridge,
shows a complex summit caldera about 60 km across, the multiple overlapping craters
and prominent terraces indicate the volcanic nature of the large mountains. Ascraeus
Mons protruded through the planetwide dust storm as a dark spot, and in December
1972 it became the first clearly identified volcanic structure on Mars. The revelation
of volcanoes on Mars thus overturned the Mariner 4, 6. and 7 thesis that Mars was a
dead planet. — H. Masursky
13
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(9°S, 120°W: IPL 1633/004651. 492/141002)
Arsia Mons (preceding page ) : a shield volcano in the Tharsis Monies. A central
smooth-floored caldera 130 km in diameter is surrounded by a zone of concentric
graben. Outside the faulted zone are numerous superimposed lava-flow lobes and
sinuous channels with isolated graben areas. The flanks are partly embayed by the
surrounding plains materials. The structure is believed to be similar to Olympus Mons
but somewhat older. The flows are shorter and thicker than those on Olympus Mons,
perhaps because of chemical differences, a lower gas content, or eruption at lower
temperatures. These flows are more similar to those on the flanks of Mount Rainier and
Mount Hood in the Pacific Northwest of the United States that are andesitic in compo-
sition.— M. H. Carr and H. Masursky
1()
(10°S, 124°W: MTVS 4182-42)
The southwest flank of the large volcanic shield Arsia Mens shows a rough, slightly
cratered terrain with large lobate lava flows trending downslope. Wind erosion has
etched the older flow fronts into a rougher terrain. The picture is about 32 km across. —
T. R. McGetchin
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(63°S, 323°W: MTVS 4238-7)
The crater above, 20 km in diameter, may be of impact origin with subsequent modifi-
cation by volcanism. The flat-bottomed depression in its middle appears to have
formed by collapse. Its central peak or dome may be a volcanic cone, as may many
of the other cone-like features nearby. Surrounding the crater are many small volcanic
cones, ranging from 2 km down to the limit of resolution, here around 250 m. —
J. E. Peterson
(38°N. 196°W; MTVS 4244^75)
A series of small domes or volcanic cones (left) rising from a flat plains terrain. The
arcuate distribution of cones suggests extrusion along the fracture system of an old
crater. Note the small crater on the summit of a cone (arrow). The cones are 3 to 7
km in diameter at their bases. The intracone plain appears to consist of overlapping
lava flows covered with a mantle of finer material (windblown debris or volcanic ash)
which subdues the flow fronts and other relief features. — D. B. Potter
19
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fi'vu
^*;,
(22°N, 97°W: MTVS 4187-90 )
Three volcanic domes (left) near Alba Patera. The dome of Uranius Patera (upper
left) has collapsed, creating a large complex caldera. Ceraunius Tholus has a sinuous
channel leading down from the caldera to a closed depression at the base of the dome.
A third dome. Uranius Tholus, is seen at left center. Note the series of parallel, closely
spaced fault valleys in the bottom of the photo. — D. B. Potter
(24°N, 98° W: MTVS 4271-.51)
A sinuous channel, about 1 km wide, occurs on the flank of the volcanic cone Ceraunis
Tholus. The summit caldera wall was breached and the channel eroded when fluids
drained from the caldera basin (off right) to the closed depression at the foot of the
cone. The mouth of the 40-km sinuous channel seems to grade into a deltalike deposit.
Many smaller sinuous channels cross the flanks of the dome, and several channels show
distributary deposits at their lower ends. Presumably, the channels are related to vol-
canic activity, but their overall characteristics are also similar to fluvial channels. —
H. E. Holt
(25°N, 213° W; MTVS 4298-44)
Elysium Mons is a symmetrical shield volcano (above) approximately 225 km across,
with a small central caldera and numerous fractures radial and concentric to the shield.
Several channels and lines of craters in the flanks of the shield appear in high resolu-
tion photographs. Two incomplete concentric fracture rings surround the shield, one
at a radius of 175 km and one at 320 km. Similar concentric fracture systems occur
around other Mars shield volcanoes. — M. H. Carr
(25°N, 213°W; IPL 7386/014900, 7386/020050)
The summit area of the Elysium volcanic cone (right) shows a well defined radial
pattern of material on the slopes surrounding the central crater. Several small chains
of rimless pits are on the right flank of the cone. The crater rim is broken by several
sinuous lava channels. The features in line with the lava channels in the lower part of
the photo are possibly collapsed lava tubes. The flat floor of the crater suggests that
it contained a lava lake. — J. W. Allingham
22
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ijip.
t* ¥.
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fr^ ■ 'Ijl
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„ •«:fc^
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=^- T-
{31°N, 210°W: MTVS 4298^7)
A small caldera (left) 10 km wide on the flanks of Elysium Mons. The caldera shows
multiple collapse depressions and several fine channels. Lines of small volcanic craters
are arranged along radiating fractures (lower right). Like the sinuous rilles on the
Moon, these lava channels start in a source crater and become narrower and shallower
downslope. Terrestrial iaval channels have similar forms. — H. Masursky
(32°N. 211°W: IPL 7386/023416)
The edge of the Elysium dome shows relationships that typify the contacts of volcanic
domes with the surrounding plains. A low escarpment may occur as in the bottom of
the frame, or the radial channels on the flanks may be truncated when they dip be-
neath the surrounding materials as in the upper center of the picture. Low escarp-
ments outline a series of lobate flow sheets extending from a crater (probably volcanic)
about 9 km across. The lobate flows are very similar to basaltic lava flows on the Earth
and Moon. — M. H. Carr
25
3
Mysterious Canyons
One of the most spectacular revelations of Mariner 9
was the system of huge canyons in the equatorial region
of Mars. These extraordinary features, up to 200 km
wide, thousands of kilometers long, and possibly as much
as 6 km deep, represent a significant phase in the planet "s
evolution.
The system of canyons, Valles Marineris, extends
5000 km along the equatorial belt. Some of the dark
markings that have been mapped for a century from
terrestrial telescopes coincide with the floors and walls
of these huge canyons. The nature of these markings re-
mained hidden until thev were pictured by Mariner 9.
The canyons consist of a series of parallel depres-
sions characterized by steep gullied walls and a sharp
brink at the lip of each canyon. The elongation of indi-
vidual depressions is parallel to the trend of the entire
belt. Walls of the canyons are rarely smooth. Most of
them exhibit features ranging from broad open embay-
ments to complex branching ravines and gullies. Some of
these gullies have dendritic drainage patterns and extend
back into the surrounding uplands for distances of up to
1.50 km. Knobs, spurs, and other irregularities suggest,
along with different degrees of dissection, some degree of
inhomogeneity in the material forming the canyon walls
themselves. The canyon floors generally lack craters, sug-
gesting either relative youth of the floors, or the effects
of some erosional process that obliterates all traces of
craters.
A moderate sprinkling of craters appears on the up-
lands surrounding the canyons: some of these craters
have broken, jumbled, and apparently downdropped
floors. Another canyon-related feature is the presence of
linear chains of rimless pits, probably of collapse origin.
It seems that craters and pits predating the canyons have
served at least partly as sites for downward collapse that
lead to the formation of the small parallel canyons.
What created the canyons? The parallelism of indi-
vidual canyons and the parallel trends of pit chains and
smaller fault valleys or graben implies a strong degree of
control by regional structural patterns. The blunt ends of
the canyons suggest that the widening and lengthening
of them by wall recession must have been a factor in their
formation. Jumbled masses of rocky debris piled on
canyon floors at the bases of numerous U-shaped gullies
indicate that mass slides, slumps, and debris avalanches
must have been a factor in shaping the canyon walls.
The major obstacle to any convincing explanation of
the origin of the canyons is: How was the bulk of the
material originally present in these enormous chasms
removed? There is no obvious way to transport debris
out except by wind. Yet the amount of material to be
transported is so great as to cast doubt on the effective-
ness of this mechanism operating by itself. The disposal
of such vast amounts of material remains a problem. —
J. F. McCaulev
27
I'
1-^
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GRAND CANYON OF ARIZONA
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The great canyon system, Valles Marineris, more than 5000 km long and at least 6 km
deep, dwarfs any stream valleys on the continents of Earth. A minor side canyon is
similar in length and depth to the Grand Canyon of Arizona (inset) . Features on Earth
most closely comparable in size to Valles Marineris are the Rift Valley system of Africa
and related rift valleys on ocean floors. As with Earth's rift valleys, Valles Marineris
may have been formed where the crust of the planet has pulled apart. Pieces of the
crust that form the floor of the canyon probably have subsided along faults. Subse-
quently the rim of the valley has been sculptured by mysterious processes of erosion.
The intricate system of canyons extending back from the rim may have been developed
during melting and evaporation of subsurface ice. — E. M. Shoemaker
< C
V.
.« <e
_,*
'1
(8°S, 84°W; MTVS 4144-87)
The s])ine-like ridge seen running through the center of the canyon above is located in the
far canyon on the facing page. Also notable are angulate dendritic tributaries on the wall and
large landslide alcoves (bottom). — R. P. Sharp
(5°S,86°W; MTVS 4191-45)
The parallel nature (right) of elements in the canyon system is revealed by this view of
two canyons with scarred and gullied walls. A chain of pits on the remnant of upland sepa-
rating the two also parallels the canyons. Landslide debris is evident in the canyon floor at
bottom right. The surface reflectivity variation is due to changes in the slope near the rims
of the canyons. This section of canyon is 440 km long. — D. T. McClelland
30
«
(13°S, 61°W; IPL 1616/212555)
This high resolution view, about 35 km in width, of the wall of Coprates Chasma
shows ravines and narrow branching divides that lie beneath a series of sharp crested
alcoves. Although these features seem to resemble at first glance typical "badlands,"
topography of the kind produced by episodic cloudbursts in arid regions, closer in-
spection reveals another possible origin. The bottoms of the gullies are not intercon-
nected and individual divides interrupt one another. Thus the pattern is not the same
as that generally produced by running water but is more similar to that produced by
mass wasting or gravity sliding of loose materials on oversteepened slopes. — J. F.
McCauley
(7°S, 85°W; IPL 1354/184219)
The steep headwall. scarred by possible dry avalanche chutes at its rim. rises several
kilometers above the jumbled landslide topography on the floor of the trough. The
smooth band below the headwall may be accumulated talus deposits. Slides like this
are locally common on trough walls. They might have resulted from undermining by
removal of ground ice by evaporation or by melting under different climatic condi-
tions. This image is about 42 km wide. — R. P. Sharp
(5°S. 77°W: IPL 1628/204400)
A blunt-ended trough (left) in Valles Marineris. Ophir Chasma, was captured in this
magnificent picture, the width of which covers about 400 km. Swirl pattern on the
floor of the trough may reflect outcrop of dissected floor deposits. Smaller troughs and
lines of pits extending westward from the headwall suggest initiation of troughs along
fractures or structures in crust. — R. P. Sharp
(13°S. 110°W; IPL 1348/223600)
The pits (above) at the right of this canyon suggest one possible method of enlarge-
ment of the canyons by collapse and drainage of surface material into what must be
a cavernous or porous subsurface. Thus the troughs may expand along lines of these
pits as well as by erosion of the walls as seen in the vertical chutes here and in the
other numerous examples of wall erosion seen in this section. This picture is about
40 km in width. — J. W. Aliingham
(22°S, 254°W; MTVS 4295-79)
These box canyons (right), in Hesperia Planum, display parallel trends that suggest
they may have developed along fractures. They were clearly formed before the large
number of local small cratering events. — D. B. Potter
34
(6°S, 105° W; MTVS 4187-45)
This "labyrinth" occurs at the western end or origin of Valles Marineris as seen in this low
resolution frame some 400 km across. It is characterized by smooth-walled gaping depres-
sions and chain craters that partly surround large flat-topped mesas. Long, narrow linear
graben also lace the area; many of these are cut bv the steep depressions. The grossly polyg-
onal pattern of the chain craters and elongate depressions is very reminiscent of that pro-
duced bv doming on Earth but it is very much larger in scale. This region is nearly coincident
with a broad swelling of the Mars surface that appears to be several kilometers higher than
the surrounding plains. — J. F. McCauley
(1°S, 76°W; IPL 1628/210149)
Deadend: This 300-km-long canyon (left) is completely enclosed. It lies somewhat to the
north of Coprates Chasma. Ravines and gullies mark the wall on the right while the left wall
has shallow alcoves with hummocky landslide material at the base. The uplands show a range
of crater size and a set of parallel fractures. — J. W. Allingham
37
^'
^i?'f!ij
(24°N, 62°W; IPL 1356/120125)
A mesa-like plateau occurs in the Lunae Planum region. Prominent scarps separate it
from adjoining lowlands, which are shown in regional pictures as an extensive valley
complex. The regular scalloping along the upper edge of the scarps suggests headward
mass wasting and eolian fluting. The plateau section shown here is about 60 km in
length.— T. A. Mutch
39
4
Channels
Numerous channels, ranging from broad sinuous
channels nearly 60 km wide to small ( less than 100 m
wide I narro'.v dendritic channel networks, occur over
local and widespread martian regions. Many of the chan-
nels appear remarkably similar to stream channels on
Earth. Sinuous channels containing discontinuous mar-
ginal terraces, teardrop-shaped islands, and braided
stream channels and bars, must have been eroded by
fluids.
The channels of Mars have been grouped into four
general types. Three types have characteristics that imply
a fluvial origin: broad and sinuous channels, narrow
channels with tributaries and braided streambeds, and
closely spaced coalescent channels. A fourth variety has
characteristics that imply molten lava channels.
Some of the largest channels, which are 30 to 60 km
wide and up to 1200 km long, appear to originate in the
northern plateau lands and flow northward into the Chryse
region. As the complex array of the broad, sinuous chan-
nels empties into the flat low Chryse area, the channel
floors show characteristics that confirm the northward
direction of flow consistent with the regional slope of the
surface. These channels resemble features produced by
episodic floods on Earth. The large Chryse channels have
potential sources of fluids in the chaotic terrain, and the
tributaries are proportional in size to the area of chaotic
terrain they drain. Catastrophic melting of ground ice
could form both the chaotic terrain and the giant flood
channels in a single event.
Narrow, sinuous valleys, some with many tributaries
forming dendritic-like patterns, lie on high level plateau
surfaces such as Lunae Planum and Memnonia in the
martian equatorial region. The fluvial character of these
channels, combined with the lack of apparent source
areas, requires the surface collection of fluids into inte-
grated channels along with surface erosion and subse-
quent deposition in alluvial basins. An intermittent at-
mospheric source for channel erosion appears logical and
is supported by the presence of channels which head very
close to ridge crests.
Local networks of very small coalescent channels are
widely spaced across the equatorial region. Northwest of
Hellas Planitia, networks of coalescent channels run down
the sides of many craters. Their form again suggests a
precipitation collection system and such an origin re-
quires widespread intermittent precipitation across the
equatorial zone.
Another type of channel, associated with volcanic
centers, is the lava channel or collapsed lava tube. These
channels start on the flanks of volcanic domes and shield
volcanoes but become less defined downslope. This rela-
tionship is the opposite of that generally observed in
stream channels.
Most martian channels are indicative of past erosion,
transport, and deposition of surface materials that only
running water could produce. Under present martian at-
mospheric conditions, liquids would not exist on the sur-
face except during rare conditions. — H. E. Holt and
M. A. Sheldon
41
.(Ti
s
(6°S, 150° W; MTVS 4258-35, 4258-39)
The photomosaic (above) of the lower part of the Amazonis channel in Mangala
Vallis shows complex braiding such as streams produce in arid environments on Earth
bv depositing suspended sediment rapidly and intermittently. The streamlining of the
"islands" very strongly implies formation by running water. Patterns like this have
not been observed in lava channels on the Earth or Moon. The cuspness of the channel
floor indicates that it was formed in geologically recent times; other martian channels
are cratered and degraded as though much older. The crater seen along the right
margin is about 20 km in diameter. — H. Masursky
(31°N, 229°W; IPL 1441/152627)
The channel at left (about 45 km wide I represents a sinuous muUi-channel course
containing discontinuous marginal terraces, teardrop-shaped islands (blunt ends face
upstream) and macro braided channels. The character of this channel indicates that
it might have been eroded by fluids. This channel arises in a hummocky area and per-
haps the fluids resulted from melting of ground ice or permafrost. The only terrestrial
examples of such large sinuous channels occur in the channeled scablands of the
Columbia Plateau in the United States and the Sandier plains of Iceland, where release
of great volumes of water resulted in catastrophic erosion. — -H. E. Holt
43
(23°N, 68° W; IPL 1628/143620)
(22°N, 73° W; MTVS 4297-7, 4297-15)
A 700 km length of a southern channel in the Kasei Valiis is seen below. The flow direction
of this channel is eastward into the Chryse Planitia. An area in the lower part of the photo
(partly concealed by a dark circle produced in the Mariner television system) is shown in
the high resolution mosaic at right (approximately 75 km wide I. A dendritic canyon sys-
tem ap])ears to have developed along an angular fracture set by headward growth. Note the
smooth-floored channels. Wind scour has etched relief features across the upper plateau
level. The ejecta from the large crater form a distinct bench and are believed to be accentu-
ated by the greater resistance of the ejecta blanket to wind erosion. — H. E. Holt
.yT«^>
y. •'N ^ >
j-^-AllBBfiftkH
(29°S, 40°W; IPL 434/211030. 7462/40724. MTVS 4158-871
The channel above is about 600 km long and 5 to 6 km wide. The lower reaches (top
left) resemble the sinuous rilles of the Moon: the upper portion (top right) is more
reminiscent of entrenched desert arroyos on Earth. The meandering and dendritic
form of this channel is convincing evidence that a fluid once flowed on and eroded
the planet's surface. — H. Masursky
(20°S, 184°W; IPL 454/200454. 454/2031101
This pair of low resolution photographs (left) shows a sinuous valley. Ma'adim Vallis,
about 700 km long. The valley resembles shorter sinuous rilles on the Moon. The pre-
vious existence of fluids is strongly implied by the widening and deepening toward
the mouth of the channel and the multiple branched tributaries toward its head. Water
could not exist in the present climate of Mars, so a different climate in the past is
suggested. — H. Masursky
47
mmm'
(7°S, 151°W; MTVS 4294^20, 4294-16, 4294^12)
Middle section of the Amazonis channel in Mangala Vallis where direction of flow is
from right to left (south to north). The braided channel at right converges into a
slightly sinuous main channel, 2 to 3 km wide, containing large bars "and streamlined
islands along the streambanks. Several levels of stream terraces occur along the east
bank (top side of channel) which indicate several stages of stream erosion. The stream
terraces, bars, and braided channels suggest that the streambed was eroded by run-
ning water where the quantity of stream flow fluctuated, perhaps becoming an inter-
mittent stream. The individual frames cover an area about 30 by 40 km. — H. E. Holt
(45°N, 116°W; MTVS 4182-96)
The frame at right, about 60 km across, shows the eroded, undulating surface on a
flank of Alba Patera. The fine textured dendritic pattern of deep gullies suggests
erosion in unconsolidated material. An atmospheric source of water is suggested by
the closeness of the channel heads to hill crests and by the presence of channels on
both sides of elongated hills. Spotty distribution of such channels on the martian
surface may have a climatic basis or merely be ascribable to obscuration of many
gullies by wind erosion. — H. Masursky
«^vS'v
Vd
»
'*%''m
n
pi
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1
1
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m
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/
f36°S, 248°W; MTVS 4244-27, 4244-31)
The gullies on the inner wall of a 35 km wide impact crater, northeast of Hellas Pla-
nitia, suggest erosion bv fluids. The origin of the sullies near the summit of the inner
wall does not exclude melting ground ice as a source of fluid. The spur leading from
the right rim mav be of volcanic origin, as suggested by the multiple sinuous linear
features and by the conical peak (arrow I at the junction of the rim and spur. In the
bottom right of the picture, a small steep volcanic cone (arrow) having a barely
discernible summit crater is visible. It is part of an east-west array of similar small
conical hills, that is perhaps a volcanic chain. The channel nearby is a tributary to a
major 1300 km long channel which drains southwestward into Hellas. — D. B. Potter
(9°S, 330°W; IPL 7243/111916)
Gullies have eroded into the rims of old impact craters (below). Picture width is
about 330 km. The patterns resemble gully svstems on moderate slopes in terrestrial
deserts, and may have been formed by runoff of precipitation. — M. A. Sheldon
'^iS.'^Ws
(38°N, 330° W)
This mosaic of low resolution photographs (above) shows the margin of a heavily
cratered upland and the northern lowland that at the time was partially covered by
clouds of the martian north polar hood. The edge of the highland is dissected by many
sinuous and anastomosing channels that apparently are eroded into the highland. The
channels shown here and those near Alba are at 45°N, the farthest north that channels
have been perceived on the planet. The most abundant channels on Mars lie about
10° south of the equator. — H. Masursky
(6°N, 22°W)
The channel in this mosaic (right) of an area associated with collapsed terrain
descends north into the Chryse Planitia. The Chryse lowland is a low part of the
martian surface and a part of the lowland that girdles the planet. The channel slopes
northward about 5 meters per kilometer for 1200 km and is about 30 km wide. It
may have been produced by release of water from chaotic terrain near its head by
melting of permafrost. The channel is degraded (that is, some braided forms are vis-
ible) and somewhat cratered. indicating an intermediate geologic age. — H. Masursky
52
MM''^^'
(8°S, 151°W; IPL 1691/160649)
A complex of meandering valleys (left) cut through cratered terrain and debouch
onto smooth plains in the upper part of the picture. As the valleys are traced down-
slope, irregular dendritic furrows coalesce to form a few major channels. — T. A. Mutch
(7°N, 45°W; IPL 1634^134231)
On the edge of the Chryse Planitia, canyoned terrain (below) shows prominent chan-
nels and rilles. The conspicuous light-dark boundary divides areas of unequal crater
density. The lighter area has fewer craters; hence, it is probably a younger surface
and it may be composed of a surface covering of fine particulate material that is being
redeposited after erosion by the channels. — E. A. King, Jr.
5
Fractures and Faults
Fractures and faults are abundant on the martian
surface. Faults extending radially from craters and iso-
lated fractures thousands of kilometers long indicate the
response of the martian crust to changing stress condi-
tions.
Surface fractures associated with large shield vol-
canoes and domes may result from the upwarping of the
crust; possible later withdrawal of subsurface magma and
concomitant collapse may produce faults. Radial and con-
centric fractures are also present in crater fields, and are
due presumably to the tremendous shock of impact and
subsequent readjustment of the crust.
The most common fracture-related feature is the
graben: a valley formed when the area between two
approximately parallel faults drops down relative to the
areas on each side. Many grabens are radial to the Thar-
sis volcanic field, suggesting that the broad uplift of the
volcanic field and the attendant stretching produced many
sets of faults and, subsequently, grabens.
Fractures in volcanic regions commonly serve as
weak or dilatant zones through which lava can escape to
the surface, giving rise to an alignment of volcanoes or
flow features. These alignments serve as an indication of
now obscure fractures. Fracturing and faulting of the sur-
face may also determine the trend of an escarpment of
canyon. Such structural control is indicated by the occur-
rence of linear escarpments, which commonly form inter-
sections with other escarpments. — J. W. Allingham and
J. S. King
57
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=«fi
(40°N, 108°W; IPL 1950/95214, 1950/130813)
A system of graben (above), partly deflected around a volcanic complex, form a ring
about 650 km across. Part of the system is buried under volcanic material. At least
four parallel, narrow rilles (arrows) cut across the graben system. These rilles, or
crater chains, probably are linear arrays of volcanic vents. The longest rille shown is
more than 400 km in length. Note that some graben are arranged en echelon. — J. E.
Peterson
(38°N, 104°W; IPL 1428/223550)
A detailed narrow angle view (left) of part of the graben system shown above (about
60 by 80 km). Muhiple graben interrupt sinuous channels. Many fresh raised-rim
craters are younger than the broken surface. A linear crater chain is present at upper
right. — J. S. King
61
(17°S, 110°W; IPL 1563/130615)
The intersecting and offsetting relationships between faults (right) in this high resolu-
tion view of part of the area shown below indicate the relative times and directions of
movement of the faults. For example, graben A is olfset by fault B, which is in turn cut
by graben C. Thus A must be the oldest of the three, and C is the youngest. Fault B is a
strike-slip fault (a fault which has lateral rather than vertical displacement). The
crater is 7 km in diameter. — J. E. Peterson and H. Masursky
(15°S, 108°W: IPL 1108/144725)
A system of subparallel fault lineaments trending northeast to southwest clearly define
a family of graben (regions which have been down-dropped relative to surrounding
terrain ) . A second less obvious and older system intersects these. The faulted area is
smooth plain material with only a few relatively young craters superimposed. — J. S.
King
I^Hifci;.
(31°N,81°W; IPL 1434/180111)
Complex system of graben near the Tharsis Montes (left) showing some graben offsetting
older graben. The ejecta blankets of large craters partially cover some graben in the
lower right of this picture, indicating an early age for much of the fracturing. Fluid flow
in larger flat-bottomed graben may have modified walls and deepened valleys. Note the
hanging valleys (arrows) on the sides of the deepest graben, which is 2 km wide. — J. W.
Allingham
(38°N, 140°W; MTVS 4256-60)
A high resolution view (below) shows the gradual fading of the graben into the plain
and possible evidence of fluvial modification of the graben. A second set of faint graben
crosses the more prominent set. Note the tiny conical volcanoes (center) adjacent to
the faults bounding the grabens. The area is about 45 km wide. — J. W. Allingham
65
(21°S, 106°W; MTVS 4184r-90)
This fractured plain is located east of Olympus Mens and north of Ascraeus Mons.
The pattern is almost certainly controlled by a major set of north-south trending frac-
tures, Claritas Fossae. The impact crater in the fractured plain is about 20 km in
diameter. — J. E. Peterson
(16°N, 142°W; IPL 497/191619)
Grooved terrain forms a discontinuous aureole around Olympus Mons (right). It con-
sists largely of closely spaced low ridges and intervening linear troughs that in high
resolution pictures appear to have been wind scoured. The troughs almost surely repre-
sent a complex array of fracture zones that are less resistant than the surrounding mate-
rials to wind erosion. The origin of this terrain and its relation to Olympus Mons re-
mains a puzzle. Some investigators have suggested that it represents an early outpouring
of lava or ash from Olympus Mons that have since eroded back to the pronounced scarp
that now surrounds this enormous volcanic edifice. The picture is about 365 km wide.
—J. F. McCauley
66
— ' ''-.* ■
6
Escarpments
Long, steep cliffs occur on the surface of Mars. They
are from 1 to 4 km high, and range up to several hun-
dred kilometers in length.
Many escarpments have complex configurations and
scars that suggest that some form of erosion has caused
the scarp face to recede at the expense of the uplands.
Numerous U-shaped chutes in the upper reaches of escarp-
ments are similar to the scars left by debris avalanches
on steep terrestrial slopes. Lumpy mounds of material
below alcoves or gullies are indicative of debris slides
or slow downhill movement. In regions bounding chaotic
terrain, huge blocks that often retain their original flat
tops have slumped downward and outward from the edges
of escarpments.
In contrast to the deeply embayed and scarred cliffs,
there are also long escarpments with straight, sharp
brinks and few scars. Because of this configuration, this
form of structure is thought to follow faults or fractures,
and to have undergone little recession of the face.
In the polar and near-polar regions some scarps seem
to be a product of erosion of layered material that mantle
older, cratered terrain beneath. This observation suggests
that Mars may have undergone alternating cycles of dep-
osition and erosion, the latter attended by the develop-
ing of retreating scarps. — R. P. Sharp
71
(15°N, 130°W; MTVS 4265-48)
The southeastern portion of the Olympus Mens escarpment (above) shows a well de-
fined base and generally a sharp rim with apparent slump scarps and terraces. The
fluted, steep, upper part is partially covered by huge landslides or lava flows. The
escarpment varies from 1 to 3 km in height. Residual block-like mesas indicate the
remnants of a higher terraced surface on the flank of the volcano. — D. B. Potter
(18°N, 134°W)
The great escarpment (left) around the base of Olympus Mons, approximately 1500
km long, resembles a wave-eroded seacliff on a terrestrial volcanic island, but is not so
easily explained as there are no martian seas. The escarpment appears sharp over
more than half of its length; the remainder appears subdued. In a few places the
scarp is absent, probably covered by lava flows or huge landslides. The origin of the
escarpment is uncertain, but probably involves a combination of such processes as
mass wjisting and eolian erosion. — J. E. Peterson
73
(2°N, 111°W; MTVS 4229-51)
A detailed view of the northeast flank of Pavonis Mons (below I shows many features
characteristic of collapse between fractures which are called graben. The graben trend
northeastward, parallel to the Tharsis Montes. Rock chutes and ridges have been modi-
fied by wind action. — J. W. Allingham
(9°S, 69°W; IPL 7224/160459)
The elongate flat-topped highland area (right) is comparable to the mesas common in
arid regions on Earth. This mesa, rising 2 to 3 km above the floor of the huge Coprates
Chasma, is about 400 km long and 150 km wide and connects (not shown) to an ex-
tensive plateau area north of the canyon. Sculpturing on the steep slopes of the mesa
indicates downslope movement of material by landsliding, leaving the characteristic
U-shaped chutes. The apparent absence of landslide deposits below the chutes suggests
their removal by wind or running water. The top of the mesa is extensively transected
by faults, some of which occur in facing pairs so as to produce long, narrow troughs or
graben.— G. E. McGiU
74
•4-
X
W.i;u"jjnJ:!«. :!3:-'iiliL;dl£U;'.l:
(13°S, 71°W; MTVS 4195-33)
This arcuate escarpment, several kilometers high, is a portion of the south wall of
Valles Marineris at one of its widest points, Melas Chasma. Erosion by mass wasting
appears to be the dominant process involved in the escarpment retreat. Debris ava-
lanche chutes are abundant along most of the scarp. Note the long ridge extending
about 80 km into the canyon. — J. E. Peterson
(12°S, 50°W; IPL 7464/235907)
The sharp rim edge along the northern edge of the equatorial plateau (above) indicates that
resistant rocks underlie the plateau. The escarpment is 1 to 2 km high and alternating resist-
ant and nonresistant rock layers are exposed on the cliff faces. These may be alternating
lava flows and pyroclastic rocks as these exposures are not too far from the great volcanoes
that may have acted as the source for the rocks. The rock layers may be from 100 to 200 m
thick. The few impact craters on the surface of the plateau imply that it is geologically a
young surface. — H. Masursky
(5°S, 85°W; MTVS 4275-36)
Detail of Valles Marineris wall and edges of the plateau. Note the apparent raised rim of the
plateau and occurrence of bedded outcrops just below the rim. The picture is about 63 km
wide and the escarpment is several kilometers high. — D. B. Potter
78
(41°S, 258°W: IPL 1445/105008)
This isolated bold mountain remnant on the plains at the east edge of Hellas Planitia
is approximately 35 km wide. Its sharp ridges and spurs have a branching pattern
indicating equal erosive attack from all sides. The steep upper slopes show mass wast-
ing chutes and narrow tongues of material suggest some form of mass movement.
Broader tongues of material occur along the western base. Around the base of the
mountain is a wide apron sloping gently away from the mountain. This suggests slow
mass movement of granular material over a long period of time. — D. B. Potter
\
7
Fretted and
Chaotic Terrains
Fretted and chaotic terrains are lowland topographic
forms on the martian surface which may be in part the
product of related genetic agents. Fretted terrain is char-
acterized by smooth, flat lowland areas with many flat-
topped buttes and mesas resembling those in the western
United States. Chaotic terrain exhibits rough floor topog-
raphy of jumbled large, angular blocks. Both terrains are
separated from cratered upland areas by escarpments
having complex configurations.
A striking characteristic of fretted terrain is its ir-
regular border pattern. The steep escarpment is smoothly
sloping and free of slump blocks and typically traces a
ragged course with deep embayments, projecting head-
lands, and numerous shallow scallops. The lowland floor
of the fretted terrain is generally smooth, showing only
a few scattered craters and low swells and swales.
Some areas of chaotic terrain are sharply bounded
by an abrupt escarpment of irregular configuration, while
other boundaries exhibit a transition from slightly frac-
tured upland through a highly fractured zone to a jumble
of irregular blocks. The vertical relief of escarpments
seems to range between 1 km and 3 km. They are higher
than most escarpments bounding areas of fretted terrain.
The most distinctive feature of chaotic terrain is the
rough-floor topography consisting of an irregular jumble
of angular blocks up to several kilometers wide and tens
of kilometers long, many bearing remnants of the rela-
tively smooth upland surface on their tops. At some sites,
the shape of the blocks appears to be controlled by inter-
secting sets of fractures resulting in blocks of almost
equal dimensions. After formation, the blocks appear to
undergo continuing breakdown and reduction in size,
eventually being completely destroyed and leaving a flat,
smooth floor similar to that of fretted terrain.
Fretted terrain, clearly developed at the expense of
older cratered uplands, appears to be among the youngest
of the martian landforms. The smooth floors of most areas
of fretted terrain are only sparsely cratered, mostly by
small, new craters. Chaotic terrain is judged to be equally
youthful on essentially the same basis. Closely adjacent
areas of fretted and chaotic terrain cannot be too differ-
ent in age. However, the seeming paucity of craters within
areas of chaotic terrain may be a result of difficulty in
recognizing small craters within the chaos of jumbled
blocks.
Subsidence and slumping having played a part in the
development of chaotic terrain. Since these are usually
initiated by the removal of subsurface material, the prob-
lem of the origin of chaotic terrain becomes one of identi-
fying the material removed and the process, or processes,
which accomplished the removal.
The development of fretted terrain is thought to be
initiated by some structural break in the old cratered
uplands. Once an escarpment is formed, it recedes by
some type of undermining or sapping mechanism. The
erosional removal of debris, perhaps by the wind, leaves
a smooth, flat floor and isolates island-like buttes and
mesas. The bounding slopes of these outliers also recede,
reducing them in size until they disappear entirely. —
R. P. Sharp
83
^^^^^^^^^^^^^Kf^^^^^^- ^': W^*-m
il
'-^^
.^m^ V
:^ I.
(44°N, 330°W; IPL 1417/224259)
A close-up view of erosional outliers in an area of fretted terrain. The height of the
prominent features is at least 1 to 1.5 km. The undulating plain shows numerous
swells and swales. The young, raised rim crater is about 3 km across. — R. P. Sharp
(43°N, 313°W; IPL 1651/154245)
In this fretted terrain (left) at mid-latitude in the northern hemisphere, a relatively
smooth lowland is separated from the old cratered upland by abrupt cliffs at least 1 to
2 km high. Mesa-like remnants and flat-floored chasms penetrating far into the upland
are characteristic. This terrain is regarded to be a product of cliff recession caused by
an undermining process operating at the cliff base. Material shed by the cliffs has
been removed, probably either by fluvial transport, under different climatic condi-
tions, or by eolian deflation. — R. P. Sharp
85
(3°N,37°W; IPL 7350/165312)
Association of chaotic terrain (upper right, facing page) with flat-floored steep-walled fea-
tures that are characteristic of fretted terrain suggests some common genetic influences. Note
the arcuate slump blocks at the lower edge of the chaotic area (arrow). The flat-floored
chasm leading to the left may have been modified and widened by the recession of walls as a
result of undermining or it may represent a channel carved or modified by a huge flood which
burst forth from the area of chaotic terrain. — R. P. Sharp
(1°S, 20°W; IPL 7059/162910)
(4°S, 20°W; IPL 1411/212107)
Views of chaotic terrain (below), formed by the collapse of an old crater upland when its
underlying support was withdrawn. In the top photo, a broad, seemingly scoured channel can
be seen emerging from the chaotic area in the upper right corner; the photo at bottom shows
a close-up view of the broken blocks in the right central part of the top photo. — R. P. Sharp
'f'>\1
Liii;;*.
Md?
* ti
m
"'::&im
a"*^
&.f'
••!!!!fHi»w!";:^Bfe<iji
-.i'-^ ' ^4»i 1-
'!H»
LLiiiJt]iai<:£r
(3°N, 28°W; MTVS 4203-60)
This moderately cratered surface extends over several thousand square kilometers.
Three areas shown in this photo consist of complex mosaics of broken surfaces ranging
from over 15 km across down to the resolution limit of several hundred meters. The
massively fractured and slumped chaotic terrain generally lies below the level of the
surrounding older surface. Large channels originate in the chaotic terrain area and
extend many hundreds of kilometers northward. The chaotic terrain and channels may
have resulted from removal of materials in the subsurface with consequent collapse
of overlying strata. Perhaps some form of ground ice melted, and the resulting liquid
drained away forming the large channels. However, physical/chemical processes
needed to produce such large quantities of ground ice, and later to supply large
amounts of local heat to melt the ice in a very short time span, are not recognized
topographic/geologic processes. — H. E. Holt
8
Craters
Large circular basins like those which enclose Hellas
Planitia, Argyre Planitia, and Isidis Planitia are the old-
est recognizable structures on Mars. Several of the basins
display remnants of concentric rims and radial fractures,
and appear similar to lunar multi-ring circular basins.
These great basins are believed to have been formed by
impact during planetary accretion, and thus may be
classed as ancient super-craters.
Although numerous martian craters are of volcanic
origin, the great majority of them are probably the result
of impact. The oldest heavily cratered terrain is saturated
with large craters having diameters greater than 20 km.
Such terrain occurs preponderantly in the equatorial zone
and the southern hemisphere, including the polar area,
which appears to contain many subdued craters. Small
craters are rare or lacking in the polar regions.
Most large martian craters have been modified by
subsequent impact, blanketing, and eolian processes.
Many craters are subdued, with extensive wall slumping
and infilling. They are shallow, have flat floors, and
usually lack central peaks. These characteristics probably
result from deposition of material, perhaps volcanic, after
the craters formed.
Several aspects of martian craters are noteworthy.
Many of them are doublets, nearly tangential, and about
the same size. These could have been formed by internal
processes such as the collapse of volcanic structures, or
by impacting masses that broke apart before striking the
surface. Some impact craters appear to stand on plateaus
or pedestals. This effect might have been caused if ejecta
had possessed a greater resistance to erosion than did the
general terrain material. Other martian craters may have
been caused by low-angle impact, as suggested by elon-
gate form and bilateral ejecta patterns.
In general, the cratering histories of Mars and the
Moon may have been similar. But differences in planetary
size and gravitational attraction, as well as the presence
of an atmosphere and extensive deposition of filling
material, have led to certain characteristic differences in
crater morphology. — D. E. Wilhelms
91
fJ '.M,
^
*"</ w
WM
HSIL
A
t^m '
^^'^^VP^'
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1
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(53°S,81°W: IPL 406/1927722
The double-ringed basin Lowell (left). 200 km in diameter, is most probably of impact
origin. Sharp-textured ejecta attest to its relatively recent formation. In comparison to
craters having single rim crests and multiringed circular basins, this crater is inter-
mediate in diameter and in number of rings. It shows what many older, degraded
features once looked like. — D. E. Wilhelms
... JH
KW
^
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si*t...
^^■=k
.4.
V
-•*
(46°S, 44°W; MTVS 4139-9)
This smooth plains area is the northern half of Argyre Planitia and is about 800 km
across. Careful study of this and adjoining photographs reveals concentric rings of
high, rugged terrain around the plains, similar to the multiringed circular basins seen
on the Moon. — D. E. Wilhelms
\^fi
(16°S, 350°W; MTVS 4287-24)
Typical cratered terrain (right) has both old, smooth-rimmed craters, and younger,
sharp-rimmed ones. The large one at the top is 165 km across, with a conspicuously
flat floor and slumped walls. Note the small doublet craters at lower left with central
peaks. — M. Gipson, Jr.
(5°N, 250°W; MTVS 4194-60)
This cratered terrain (below) also shows lineated features made up of plateaus and
troughs. They align radially with the Isidis basin, which is outside this image toward
the northwest. — D. E. Wilhelms
I
M'^m
■■
^1
jL iJ^^^^H
^^^H
f^.r:
i ^
gS
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Ifjl^^l
^^^^B< 'Wi^ ^1
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^HjM
^^^H
MkJ^^^^h^^^^^v
^^^K* '!f'' ■
K
^'^^■^^^^^^l
^HK<iwl
Bk ^v**' jfl
^^^^^1
^^^^^^^^H) ?i
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Bti'"'
1
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^^
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B
HI-'.
.1 •
m::
■si
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•B-l|^
fpT
'liiL.
(38°N, 343°W; MTVS 4210-66)
The sharply defined little crater in the center of the photo above is relatively young, as
attested to by its bowl-shaped floor, raised rim, and well-preserved, ray-like ejecta
blanket. Its diameter is 3 km. — J. W. Allingham
{23°N, 290°W; MTVS 4183-90)
A combination of densely and moderately cratered terrain (left) also includes popula-
tions of old craters and those of moderate age. Scale of this photo is about 450 km
across the top. Two parallel troughs occur at the bottom. — D. E. Wilhelms
97
(3°N, 304°W; IPL 1764/235027)
A continuum of crater types (above) is revealed in this picture, ranging from the
subdued, knicked one at bottom to the sharp-edged, relatively young one at top, with
its ejecta blanket and small central peak. — D. E. Wilhelms
(38°N, 335°W; MTVS 4212-66)
Impact origin (right) is probable for this 15 km crater. The hummocky texture of its
ejecta blanket suggests that little erosion has occurred since its formation. Neverthe-
less sufficient time has elapsed for several kilometer-sized craters to have been produced
in the ejecta. Many small craters can be detected in this picture down to the limits of
resolution of several hundred meters. — D. E. Gault
9
Wind -Shaped Features
Mariner 9 convincingly demonstrated that wind is
the dominant agent of erosion and sedimentation on
Mars. In addition to the great dust storm of 1971, a wide
variety of features that can be ascribed to wind activity
were found. Unlike craters on the Moon (which lacks an
atmosphere) the craters on Mars show the effects of both
eolian erosion and deposition. Most craters tend to have
flatter floors and less distinguishable surrounding ejecta
blankets. Others appear to have been once buried and are
now being exhumed by wind action. The equatorial re-
gions of Mars appear to be areas where wind erosion
predominates over deposition. This can be seen in nu-
merous examples of streamlined canoe-shaped hills, fluted
cliff faces, along with multitudinous parallel grooves on
the surface of the flat plains. Similar appearing features
are found only in the most rainless and wind-swept
deserts of the Earth. (See "Similarities: Mars, Earth, and
Moon.") The midlatitude and polar regions appear on
the other hand to be areas where deposition of fine wind-
blown material predominates. These deposits produce
vast almost featureless plains that bury earlier craters
and volcanic flows.
The changes in the surface markings of Mars have
been a puzzle to telescopic observers for generations.
Many elaborate hypotheses have been invented to explain
these in terms of vegetation, volcanic activity, or chemi-
cal changes. Mariner 9 has shown that almost all the
surface markings can be explained by wind activity.
Many of the abundant light and dark streaks are asso-
ciated with craters and other topographic features. These
frequently merge into broader mottled patterns that at the
telescope would have appeared to be continuous dark
patches.
During the Mariner 9 mission some of the streaks
actually changed shape and position indicating that they
are superficial. (See "Changing Features.") One explana-
tion is that the light areas are zones of deposition of re-
cent dust and fine sand. The dark areas are zones of
somewhat coarser and darker material where dust and
sand have been removed or were simply not deposited.
The same situation prevails in terrestrial deserts in the
lees of topographic obstacles. Some of the dark areas in
the floors of craters, on the other hand, proved to be
large dune fields, further convincing evidence for the
dynamic role of the wind on Mars. We now know that
the wind is currently sculpturing the surface of Mars, re-
moving silt and clay from some areas and redepositing it
in others. As will be seen in other sections of this book,
fluvial and glacial activity also have taken place. Thus
primarily because of its atmosphere, however tenuous,
Mars as had been surmised from the early telescopic
observations to more closely resemble the Earth than
does the Moon. — J. F. McCauley
101
(11°N, 283°W; MTVS 4186-69)
Dark and white streaks on the slopes of Syrtis Major Planitia. Viewed telescopically,
the surface of Syrtis Major Planitia is dark, and has an eastern variable edge, whose
lateral variation is enhanced by seasonal albedo changes. On Mariner 9 images, this
dark region is resolved into a series of sub-parallel dark and white streaks, which ex-
tend several hundred kilometers. In this high resolution picture (40 km wide) taken
by the Mariner 9 camera on January 30, 1972, a few weeks after the end of the 1971
dust storm, dark streaks extend from craters and unresolved point obstacles which
protrude above an otherwise smooth surface. The small streaks extend as many as 50
crater diameters beyond the crater obstacle, and invariably flare in an easterly direc-
tion. The wider and nearly continuous dark streaks in the right of the picture extend
from a large crater located outside the image. These dark streaks resemble the dark
wind shadows formed in the lee of obstacles, particularly downwind from the slip
face of transverse dunes (barchans) in terrestrial deserts, where turbulent eddies in
back-sweeping motion remove light-toned eolian sand from a darker (and coarser)
desert pavement. At the same time, sand saltates and creeps away downwind from the
barchan horns. Both processes are concomitant on the Earth, and so they are on Mars.
In support of this assertion is the digitate or serrated outline along the edge of the
widest white streak in the image. The white "teeth" along this irregular contact between
white and dark streaks point the same way as the flares in the dark streaks. They re-
semble the front of a sand sheet advancing over a barren terrestrial surface. The over-
all pattern of light and dark markings is confidently ascribed to the work of unidirec-
tional, westerly winds. — M. J. Grolier
102
^*-
..a •*
.1
■I
V^
f^
r
« i)
i^ *
^^wsf^s
(47°S,330''W: IPL 267/220940 )
(47°S, 330°W: MTVS 4228-15. 4264-15, 4264-19)
A dark zone in the floor of a crater near Hellesponti Montes is seen in the low resolution
photo above. Similar appearing dark splotches appear in the floors of many Mars craters. The
high resolution photomosaic at left reveals that the dark zone is an elliptical dune field
about 130 by 65 km in size. The dune field consists of series of subparallel ridges, 1 to 2
km apart, that closely resemble terrestrial transverse dunes. Many of the ridges appear to
have rounded crests with similar slopes on either side. This suggests that although the wind
here generally blows at right angles to the transverse ridges it may intermittently reverse its
direction so as to even out the slopes on the windward and lee sides of the dunes. The un-
usually dark appearance on what appears to be the more windward side of the dunes may be
concentrations of dark heavy minerals such as ilmenite and small dark lithic fragments. On
Mars, concentrations of such heavy minerals may have become preferentially trapped in
crater floors because of nind action. — J. F. McCaulev
(38°N, 260°W; IPL 1433/210342)
(5°N, 152°W; MTVS 4294^28)
Differential erosion of two different types around probable impact craters. Top right, a sharp-
rimmed, 20 km crater is encompassed by a radially and concentrically fractured rim unlike
that seen around any lunar crater. Similar features are known to occur in the bedrock be-
neath the ejecta of terrestrial impact craters. This suggests that wind action has completely
stripped away the original ejecta deposit exposing the shock deformed pre-crater surface. In
contrast "pedestal" craters 1 to 2 km across, also different from any lunar crater, are seen
below right. They are surrounded by sharp serrate scarps that coincide approximately with
the boundary of what would be the continuous ejecta blanket of an impact crater. In this case
the rubbly ejecta appear to have operated as a temporary "armor" acting to protect the sur-
face on which it lies while the less resistant surrounding plain was being lowered by wind
erosion. — J. F. McCauley
(71°S, 217°W; MTVS 4264-19)
Highlighted by frost, probable eolian features are seen in the specially processed high reso-
lution photograph below. The features are most likely wind blown dunes of martian sand and
dust. These dune-like features occur in craters located along the margin of the layered ter-
rain in the south polar region. The features appear to be confined by the closed topography
of the craters. The dunes are in a crater partly buried by layered terrain. Individual dunes
are approximately 3 km apart. The area shown is about 40 km wide. — L. A. Soderblom
106
r
(87°S, 273°W; MTVS 4248-12)
Flutes and linear grooves (right) in the layered terrain exposed near Australis Chasma,
south polar region. There is no polar cap shown here. Bedding is enhanced by the
contrast between the light and dark layers exposed in steep bluffs, and the sides of the
prominent ridge in the eastern part of the area. The short, finely structured striations
in the bluffs stand out in contrast against the smooth surfaces of terraces and hollows,
which are perhaps mantled with wind-blown material. Striations in the bluffs and
wider flutes on gentler slopes are parallel, and best developed on south-facing slopes.
A hill in the center of the image is grooved at one end, and beveled at the other end,
much like some terrestrial yardangs are. The erosional pattern suggests that wind ero-
sion, together with possible melting and sublimation of the underlying material, are
the processes modifying this polar landscape. Scouring here is accomplished by winds
originating near the South Pole (outside the imaged area) . — M. J. Grolier
(74°S, 7°W; MTVS 4270-24)
Irregular pits and depressions near the south polar region are shown below in this
high resolution photo. These depressions are generally characterized by flat floors and
rather smooth walls. They are very similar to terrestrial deflation hoUows formed by
the plucking and scouring action of the wind. These landforms, like the other
probable martian wind features described in this section, are many times larger
than their terrestrial counterparts, the largest known of which are in the desert of
north central China. Picture width is about 75 km. — J. W. AUingham
,>^
.\m.
'.#:':''^-''ISfc.V:-*-;t
-^i*:
■^
>>**!;*« ■■
-. ■■. *#c
(5°N, 146°W; IPL 1596/212535)
Wind etched semi-parallel grooves occur on probable bedrock in the relatively smooth.
uncratered plains of southern Amazonis. The width of the picture is about 40 km so
that the alternating, streamlined ridges and grooves are typically about 200 m in width
and tens of kilometers long. This pattern is probably controlled in part by bedrock
fractures. Similar parallel scouring of homogeneous materials does occur, however, in
the flat open parts of terrestrial deserts that are characterized by strong, almost uni-
directional prevailing winds. On Earth similar appearing wind scour features are,
however, many times smaller in size. Although the martian atmosphere is one hun-
dred times less dense than that of the Earth, the wind velocities may be on the order
of 200 to 300 km per hour. Thus the kinetic energies of particles moved by the wind
will be many times greater and the erosional effect of sand blasting a far more im-
portant geologic process than on Earth. — J. F. McCauley
111
i
10
Changing Features
Telescopic observations of Mars show that its appear-
ance changes with the seasons. As the polar cap recedes
toward the summer pole, a progressive contrast enhance-
ment between the bright and dark areas takes place. This
seasonal change starts in spring at the edge of the reced-
ing cap and proceeds toward the equator, and is referred
to as the wave of darkening. As observations of Mars
from Earth are very difficult — the attainable resolution
is about 60 km — many theories have been offered. The
darkening was once thought to represent martian vegeta-
tion responding to water vapor released into the atmos-
phere by the receding polar cap.
Such changes can now be explained in terms of
windblown dust. According to the simplest version of
such a model, a large dust storm occurs each martian
year soon after perihelion and covers most of the planet's
dark albedo markings with a thin layer of fine, bright
dust. Because of local conditions, such as topography,
subsequent seasonal winds will scour these bright parti-
cles more efficiently from certain regions than from
others. Those regions which are efficiently swept will re-
appear as dark features first.
Many of the classical variable regions of Mars, for
example Promethei Sinus, were observed by Mariner 9
to be cratered terrains liberally sprinkled with dark amor-
phous spots which we may call "splotches." These
splotches are closely related to winds, since when they
occur in craters they are usually found tucked up against
a crater wall on the downwind side of the crater.
High resolution photography provides other proofs
of the connection between splotches and Martian winds.
Some splotches show scalloped edges, a characteristic
sign of wind erosion. Sequential observations have shown
splotches to be highly variable with time. In many clas-
sical variable regions, such as Syrtis Major Planitia, the
albedo boundaries seen from Earth are determined by
a superposition of bright and dark streaks. Syrtis Major
— perhaps the most famous dark region on Mars — has
long. dark, wind-related, curved streaks trailing from its
craters. Most of the eastern boundary of Syrtis Major is
defined by such streaks, and these wind-related streaks
change with time.
During the Mariner 9 mission the dark streaks in
Syrtis Major grew. The simplest explanation is that winds
were sweeping up the bright dust that was deposited over
most of the dark material in Syrtis Major by the 1971
storm.
Mariner 9 has confirmed that true changes occur on
Mars. These changes are best explained in terms of wind-
blown dust, and do not require a biological explanation.
Of course, this does not demonstrate that life does not
exist on Mars; the only way to settle that argument is to
land on the surface and look. — C. Sagan, J. Veverka,
P. L. Fox, and L. Quam
113
(70°S, 259° W; MTVS 4211-9)
A low resolution view of Promethei Sinus (above) shows an extensively splotched, cratered
region near the south pole of Mars. This picture is about 450 km across. Variations in the
appearance of this region have been reported by telescopic observers. Note that the dark
crater splotches tend to lie on the downwind side of crater floors. A small crater near upper
center is shown at high resolution on the facing page. — C. Sagan
(70°S, 253°W; IPL 1418/143014)
This high resolution view of a region in Promethei Sinus was studied for surface variations
during the Mariner 9 mission. The scalloped appearance of the albedo boundaries is charac-
teristic of eolian phenomena — the inferred wind direction being at right angles to the scal-
loped edge. Variations in the crater splotch and in the leaf-shaped albedo marking just left
of crater, most likely due to the removal of mobile material by w inds, are shown on the fol-
lowing pages. — C. Sagan
114
^
^
S^^.'
-^i
>*
'>"'
*^r*
i.r>i*t
>.^
ii^:^':
i^gt'..v^j
(70°S, 253° W)
The dark pattern changed from rev 99 (top left) to rev 126 (top center) ; rev 126 to
rev 179 (middle row) ; and rev 179 to rev 181 (bottom row) . After the images from each
set (left and center) were similarly scaled and projected, then the two pictures were
differenced, picture element by picture element. Images on the right show the differ-
ences (Stanford AIL Picture Product STN 9167:050609, 10, 11). Thus, it is possible
to see the changes that had occurred between successive revolutions over the same
area. Each frame is about 30 km across. — C. Sagan
i(?SKj;«y«.;i,3ftjiS4
(.
(70°S, 253°W)
These comparisons show changes in the crater splotch in Promethei Sinus. Differences
between preceding views are shown at the right in each row ; the left and center views
are from (top row) revs 126 and 179; (middle row) revs 179 and 181; and (bottom
row) revs 181 and 220 (Stanford AIL Picture Product STN 0173:061109, 10, 11).
Since lighting and viewing conditions varied slightly, changes in shadows caused by
topography cannot be successfully canceled out. Each frame is about 30 km across.
— C. Sagan
Il "
.,i1«
w
-^
., ,"1
jr"-'
...N*^'
-"*"T
'iirl
Fwr^
pr
i»»
F
i«l
'ii
^ : -
r'
■¥.m
P^i^'tti^
S
^•-
.•( ■« uf*
(10°N, 283° W; MTVS 4186-69)
The eastern edge of the classical albedo feature, Syrtis Major, is outlined (left) by a
concentration of variable dark streaks. The patchy, discontinuous character of these
streaks is unique on Mars. This characteristic, as well as the tendency for the streaks
to shed off tangentially in a common direction from topographic protuberances such
as crater walls, suggests that they are produced by eolian erosion of extensive, but
very thin, deposits of bright albedo material, resulting in the exposure of dark, under-
lying, wind-resistant formations. This low resolution view is about 370 km across.
— C. Sagan
(10°N, 283°W)
The gradual darkening of Syrtis Major (above) after the 1971 dust storm is revealed
by Mariner 9 photography. The effect of the storm may have been to cover the area
with a thin layer of bright dust. Subsequent winds, blowing predominantly west to
east (the direction of the dark tails), scoured off this material, especially in regions
where wind speeds are intensified by topography. The views are from rev 155 and
rev 233; the image at right shows the difference of the two (Stanford AIL Picture
Product STN 0164:041506). The area is about 130 km across, and corresponds to the
lower left portion of the photograph on the facing page. — C. Sagan
119
(23°S, 241°W; IPL 311/210101)
A low resolution view (right), about 400 km across, of a region in the Hesperia Planum
shows numerous parallel, light streaks associated with craters. A credible explanation of
such an array of long parallel streaks emanating from craters is that fine, bright dust, trans-
ported into craters in the waning stages of the dust storm, was subsequently blown out by
high velocity winds having a prevailing direction. In any case the streaks must point down-
wind, and are natural wind direction indicators. — C. Sagan
(10°S, 107°W; IPL 1108/150842)
An area in Tharsis (below), about 160 km across, characterized by an assortment of bright
streaks showing strong evidence of an eolian streak stratigraphy. No variation in the config-
uration of these streaks was observed during the Mariner 9 mission. — C. Sagan
■■
lip
■MP-i
■.Ifii-.a*. .mi
c
|£
■4#^:r..f
(9°N, 191°W; IPL 1612/173205)
A region near Cerberus (above), about 245 km across. The prominent dark streak is
probably depositional in character. An upwind crater can be interpreted as the source
of the dark material which, carried downwind, produced the dark tail. In the process,
a part of the rim of the smaller crater appears to have been covered by dark material,
but there is also a shadow zone behind the smaller crater where no deposition occurred.
There is a similar wind shadow behind a hillock near the lower right edge of the longer
tail. — C. Sagan
(34°S, 62°W; IPL 1934/171817)
Dark crater streaks (left) stand out in this view of a region in Bosporos. This area is
about 330 km across. Some of these dark streaks are more than 50 km long, yet
remain very narrow throughout their length. Their common direction is that of the
prevalent winds in the area. — C. Sagan
123
11
Extensive Plains
Extensive, flat to gently undulating plains occur over
vast areas on Mars. They are most prevalent in the mid-
northern latitudes, and also occupy extensive areas periph-
eral to the poles and the floors of large circular basins.
These plains are nearly devoid of relief except near their
margins where they grade into other types of terrain. The
plains commonly embay or surround the adjacent terrain
as if the latter were being inundated.
Most of the plains on Mars — like the maria on the
Moon — probably formed when huge volumes of fluid
lava erupted, spread outward, and buried the preexisting
terrain. In some areas the plains are marked by incon-
spicuous lobate scarps and subdued sinuous channels.
The scarps are similar in appearance to the fronts of
many lava flows on Earth, and the channels to lava chan-
nels or collapsed lava tubes.
The martian plains have been extensively modified
by the action of violent wind storms. The plains sur-
rounding both polar regions are interpreted as a mantle
of windblown debris. A spiral pattern of light and dark
markings along the margins of the circumpolar plains
suggests erosion and deposition by strong winds originat-
ing at the poles and blowing toward the equator. As the
distance from the poles increases, the mantle of wind-
blown debris thins. The plains deposits cover cratered
terrain in the southern mid-latitudes and, except for the
large circular basins, the plains are not well developed.
In the northern mid-latitudes, however, volcanic plains
are extensively mantled. Some scattered flat plains at
higher elevations in the equatorial regions are more
densely cratered than are the plains in the basins and
mid-latitudes, and may represent an earlier plains-form-
ing episode in Mars history.
The scattered large circular basins and other low-
lying areas probably act as relatively permanent sedi-
ment traps for wind-borne debris. The polar winds trans-
port some material for entrapment and equatorial winds
carry more material to accumulate in the sediment traps.
In most pictures of the large basins of Hellas and Ama-
zonis, the plains appear to be nearly devoid of craters
and other features having topographic relief. Because of
their seemingly low crater density, the plains in these
basins have been assumed to be covered with some of the
youngest deposits on Mars.
Some plains materials, especially those along mar-
gins near the mouths of channels, may have originated
as fluvial deposits. A good example is the Chryse region
where the great Valles Marineris system empties into the
basin of Chryse Planitia. If the Valles Marineris and
other systems of canyons and channels have been formed
by fluvial action, then the plains at the mouths of the
channels would be analogous to terrestrial alluvial fans,
although on a very much larger scale. — E. C. Morris
125
JAN 23, 1972
L« '*W-
;-!>, .
MAR 11, 1972
#i'
''>V.
(14°S, 185°W; MTVS 4211-42)
Almost featureless even to the high resolution camera, this plain (above) in the center of
the Amazonis basin shows only a few small, widely spaced craters. The largest crater in upper
center is approximately 2 km in diameter and the smallest crater that can be seen is approxi-
mately 500 m in diameter. Except for three prominent craters, all craters appear very sub-
dued possibly because of a haze layer or blowing dust close to the ground, or because the
craters are partially or almost completely buried by thick wind-deposited sediments. — E. C.
Morris
(46°S, 307°W; MTVS 4167-9)
(46°S, 305°W; IPL 1351/192301)
Smoothness can be the actual nature of the surface, or can be in the eye of the beholder, or
in weather, or in the imaging system. Picture taken on January 23, 1972, shows an area of
the Hellas Planitia (80 km) with no surface detail. (The faint circular outlines are arti-
facts in the imaging system.) Picture taken on March 11 shows ridges, craters, and other
detail of the same area, indicating that a dust storm was active at the time the first picture
was taken. Historically the Hellas basin has been the site of large dust storms as viewed
telescopically and may have almost semi-permanent obscuration of its floor by blowing dust.
It was probably fortuitous that the picture taken on March 11 was at a time when the at-
mosphere had cleared sufficiently to record the detail seen in the picture. Some dust still may
have been in the local atmosphere since details are somewhat subdued. — J. E. Peterson
127
(1°N, 147°W; MTVS 4174-57)
Most of the plains on Mars probably were formed when huge volumes of fluid lava
erupted onto the surface and buried the pre-existing terrain. These volcanic plains
were subsequently buried under a mantle of wind deposited sediments. The fluted
and lobate escarpment in the center of the picture at right was probably the terminal
end of an old lava flow that has been stripped of its cover of sand and dust and eroded
by the action of the violent winds. This erosive process has also etched and enlarged
fracture patterns on top of the flow. — E. C. Morris
(17°S, 136°W; MTVS 4179-30)
Subdued escarpments (below) may be seen along the margins of some plains. They
may be the terminal fronts of ancient lava flows, partly mantled by eolian deposits.
Similar lobate escarpments are seen on the lunar maria. — E. C. Morris
T-«!!y*^
»Af -• - V lA.
li|"i|ftaM,;|ii:
It'
M M
^
FiWi 1*1
M
P^lfr*
W*'*-
i*<6i
<■
j,<fr
•;^,
:■' ^
(51°N, 263°W; MTVS 4289-48)
In northern latitudes the plains are characterized by numerous small craters, hills and
knobs, and patchy light and dark markings. The dark markings appear to create pat-
terns, almost polygonal in form, similar to patterned terrain in the Earth's polar areas.
— E. C. Morris
131
12
Polar Regions
The martian polar regions are of special interest be-
cause they contain two unusual and unique terrains,
pitted plains and layered deposits. These two regional
units are superposed on ancient densely cratered terrains
in the south polar region and on relatively lightly cra-
tered plains in the north. The uniqueness of the etch-
pitted plains and layered terrains to the polar regions
leads to the inference that their formation must involve
frozen CO2 or H2O.
The pitted or etched plains vary widely in appear-
ance, but typically are characterized by a level surface
indented by numerous pits or irregular depressions. In
places the pitted plains are being eroded, exposing the
underlying cratered terrain. The processes of burial and
exhumation do not appear to have modified the under-
lying terrain significantly.
The layered terrain is characterized by narrow,
evenly spaced bands interpreted to be ledges of outcrop-
ping strata of nearly horizontal strata. The strata are
from 20 m to 50 m high, and a sequence composed of
more than 100 such units has been measured near the
south polar region. The absence of craters in layered
terrain suggests that either it is one of the youngest units
on Mars or the most actively eroded.
The polar ice caps lie upon the laminated terrain.
Each pole has a permanent cap composed of frozen car-
bon dioxide or water and a thin ephemeral layer of car-
bon dioxide, which forms poleward of the 60° parallels
each winter and evaporates each summer.
The cratered plains are obviously the oldest units in
the polar regions because they are overlain by all of the
other units. The pitted plains are believed to have been
deposited next. Their origin is problematical, but the
most convincing explanation seems to be that they repre-
sent a thick blanket of fine dust which has settled out of
the atmosphere at the poles perhaps trapped by water
and carbon dioxide ices. Locally this blanket has since
been eroded by the wind, producing pits. Layered ter-
rain, the youngest unit, occurs within about 15° of the
poles. The obvious stratification within the laminated ter-
rain may have been caused by periodic changes in at-
mospheric conditions while the material was being
deposited. — L. A. Soderblom
133
NORTH
POLAR REGION
^
i \
c;
Airbrush renditions give a generalized overview of the north polar region and the
south polar region. They clearly show the residual ice caps and the distributions of the
various types, of terrain. The south polar region seems much more heavily cratered
than the northern one. This is probably because the north pole pictures have much
SOUTH.
POLAR REGION
■.W<y<:
poorer resolution. Erosional debris blankets which mantle terrains surrounding both
polar zones were probably derived through the continual erosion and transport of
material from polar deposits to lower latitudes. — L. A. Soderblom and T. J. Kreidler
^ NORTH
POLAR REGION
AUGUST 1972
The frost in the north polar region is shown above covering a region about 2700 km
wide about five or six martian weeks after the vernal equinox (August 1972) and at
right when nearing its minimal extent approximately two weeks after the summer
solstice (October 1972). The frost cover had a peculiar polygonal shape that became
very pronounced during the last stages of recession of the cap. It is more likely to
136
have resulted from regional phenomena than from local scarps or ridges. Regional
textural alignments could have been induced by stable wind patterns. Note the crater
at 73°N, 198°W in the mosaic at right. It trapped and shielded frost from the Sun,
leaving a large patch on its floor. — L. A. Soderblom
137
REV 11
REV 231
(85°S, 355°W; IPL 1312/023810, 7352/184744)
From November until March the south polar cap was in the late stages of its retreat, shrink-
ing to a residual cap about 6° in diameter. The conspicuous curvilinear markings seen as
bright bands in 1969 by Mariner 7, defrosted early in 1971 to become the dark bands shown
here. These high resolution photographs were taken 110 days apart by Mariner 9. In the
initial stages of its retreat the windows in the cap continually changed, but by early 1971
they became fixed and unchanging. The dark features are bare ground, where ice has evapo-
rated from sun-facing slopes. The permanent cap probably contains substantial water, if it
is not all water, because a permanent mass of frozen CO2 would collect water even from
Mars' dry atmosphere. The width shown in each photograph is about 100 km. — L. A. Soder-
blom
(89°N, 200°W; MTVS 4297-47)
The martian north polar frost cap approached its minimal extent about one-half martian
month after summer solstice on October 12, 1972. The cap is about 1000 km across. Its topog-
raphy and the curved patterns in the interior of the frost cap are interpreted as a series
of stacked, slightly concaved plates, the upper one of less areal extent, with edges that have
been smoothed and modified. The individual plates may consist of from 20 to 40 separate
layers, with an aggregate thickness of perhaps one kilometer. The outline of the residual cap
and configuration of the interior markings arise from the frostfree Sun-facing slopes along
which layers outcrop. A dark collar of rougher textured terrain surrounds the smoother polar-
layered sedimentary complex localized in the central regions of both poles. — L. A. Soderblom
(82°S, 85°W; MTVS 4247-7)
Contact between layered terrain and pitted plains (above) is shown in this photograph
of an oval mesa of laminated terrain nesting on underlying pitted plains. In several
cases, craters can be seen emerging from beneath the layered deposits along their
margins. One crater, showing only its rim, protrudes through the blanket of the pitted
plains in the upper center of the picture. The jagged pits and hollows of a pitted plain
area are dramatically displayed in the lower part of the view. — L. A. Soderblom
(71°S, 358° W; MTVS 4234^15)
Integrated pits (right) are etched into a massive layer blanketing much of the south
polar region. An underlying rough bedrock surface with partially exhumed craters is
exposed in the pit floors. Slump blocks on pit walls and dark albedo markings at the
bases of two or three sunlit walls are particularly unusual. Some pit walls are esti-
mated to be 500 m high. The plain that is shown here is being eroded by wind action
into irregularly shaped pits that resemble the markings left on a metallic surface after
it has been etched with acid. — R. P. Sharp
140
wUP
\
'%&0:.
m^
>£Nh.
-if-i';5
iid'ijf
aj ,- i'<('
M^i!
m>
U1^^
"'^■i't ^
(75°S, 229° W; MTVS 4213-21)
Polar layered terrain (left) is one of the most striking martian surface features. From
the ground the layers may look like many of the mesas in the American Southwest.
Individual layers are probably from 20 to 50 m thick. Their origin is a mystery.
Smooth, gracefully sculptured surfaces with gentle slopes are characteristic of this
terrain. The upper edges, unlike those of slopes in the pitted plains, are rounded.
Layered terrain is essentially crater free, indicating that it is of relatively young origin
or recent erosion. The seasonal frost cap is believed to play a part in the formation of
layered terrain, perhaps trapping dust particles which settle as the ice is formed. —
L. A. Soderblom
(83°S, 37°W; IPL 1403/203733)
This view of the polar cap edge shows outliers of ice resting on a mesa of layered
terrain area about 80 km wide. Slopes of uniform width and declivity facing outward
from the center of the residual cap defrost earlier than level areas because of their
inclination. — L. A. Soderblom
■■^i-
(80°S, 245°W: MTVS 4167-96)
These irregularly shaped features, located in the layered deposits of the martian south
polar region, are probably products of wind erosion. The light colored splotch at far
left is unusual in that it bears no relation to local topography. Also visible is a crater
which was at one time buried by the layered deposits, but has now been exhumed by
the wind. (Area shown is about 90 km wide.) — L. A. Soderblom and T. J. Kreidler
(86°S, 102°W; IPL 1444/131712)
Detail of the south polar cap ( right) . This picture was taken late in the mission when
the cap had reached its limit of retreat. The underlying layered terrain is revealed on
gentle slopes facing away from the pole. — L. A. Soderblom and T. J. Kreidler
144
H^:
A^g-'S.
'■#,
q^«
IS'.!'.' . a.it'.1i.«: ' A.
(83°S, 53°W; MTVS 4261-19)
In this high resolution picture, part (70 km) of the residual south polar cap is seen
resting on a mesa of layered terrain. The patchy appearance of the ice mass occurs
because it consists of a myriad of disconnected remnants. — L. A. Soderblom and T. J.
Kreidler
147
13
Clouds of Mars
The Mariner 9 view of another planetary atmosphere
showed many features that are familiar in the Earth's
atmosphere. Pressures and temperatures in the lower
Mars atmosphere correspond to those at heights of 30 to
40 km above the Earth (about l/200th atmosphere and
— 70°C). Condensation is a slow process under these
conditions, but both CO2, the predominant atmospheric
gas, and water can freeze out and clouds do occasionally
occur on Mars. The total amount of water in the atmos-
phere is very small; if condensed to liquid, a thin layer
ranging from less than 0.01 mm to about 0.04 mm thick
would form, depending on the season. Although the vapor
concentration is extremely small in volume, compared
with the Earth's lower atmosphere, the average relative
humidity on Mars is actually fairly high. Thus, water-ice
clouds do form whenever the atmosphere is intensely
cooled by lifting or by emission of radiation. Extreme
cooling, to temperatures in the neighborhood of — 127°C,
causes CO2 clouds to form.
Cooling to very low temperature takes place in the
polar regions during winter, and an extensive cloud cover
forms a "polar hood." North of about 65° latitude, a gen-
eral haze or fog of CO2 ice crystals forms in the polar air
close to the very cold ground. This cloud cover disap-
pears in late winter to reveal a surface covered with CO2
frost or snow. Between 45° and 55° latitude water-ice
clouds form at heights ranging up to 20 km. Extensive
systems of cloud waves form as the atmosphere flows over
rough underlying terrain. The waves reveal that the wind
direction is from the west at all heights at this season,
and they indicate wind speeds ranging from as little as
10 m/s (about 23 mph) near the surface to more than
60 m/s at a height of 10 km. There is a transition zone
between 55° and 65° in which large temperature varia-
tions occur, and the clouds in this region indicate large
day-to-day weather changes, similar to those occurring in
the stormy mid-latitude zones of the Earth.
Recurrent afternoon brightenings occur in the Thar-
sis region during summer, and are due to water ice clouds
which form as heated air rises up the outer slopes of the
Tharsis Montes. These clouds occur during two seasons
when the water content of the atmosphere is relatively
high. Other condensation clouds have been observed over
Argyre and Hellas, and over the north polar region in late
spring.
Probably the dust storms are the most spectacular
atmospheric events observed. These range in scale from
the planetwide storm, which obscured the entire planet
at Mariner arrival, to "small" storms covering areas of
the order of 100 000 km- (about the area of Ohio). The
latter were seen several times by Mariner 9 in the region
of winter storms along the periphery of the north polar
cloud hood, and they were also seen in the tropics. Be-
cause the dusty air is a strong absorber of sunlight these
storms influence the circulation, and the planetwide storm
showed a unique circulation regime driven by heating of
the dust-laden air. — C. B. Leovy and G. A. Briggs
149
(19°N, 111°W; MTVS 4098-S2)
(14°N, 110°W; MTVS 4098-78)
Some of the last photos received from Mariner 9 showed extensive cloud activity near
the largest volcanoes on Mars (right). A high resolution picture (above) of Ascraeus
Mons acquired at the same time showed cells suggesting convection, and the infrared
spectrometer identified the clouds as water ice. They appeared to be relatively low, and
were probably caused by air cooling as it moved up the slope of the volcano, but exchange
of water vapor with the ground or even volcanic venting could also be involved. B. A.
Smith
150
Arsia Mons*
f^i.
1.1*
Ascraeus Mons
m'^.:-:'',7r:-vm. immitiK'.
■offi*;
>i^}
,;!•'
•Ain^.
(15°N, 42°W; IPL 1765/105021)
(13°N, 42°W; IPL 1676/210508)
After the global dust storm subsided and the view of Mars from Mariner 9 was gen-
erally clear, local obscuration by streamers like those shown at left was observed.
Twenty days later the streamers were gone (above) ; the arrows point to the same
crater in both pictures. This region is about 650 km wide. Temperatures there were
high and the streamers originated along terrain irregularities where turbulence could
enhance the prevailing winds' ability to raise dust. Short-lived, localized dust storms of
this type are familiar to astronomers as "yellow clouds" and are very different from
the white clouds produced by condensation. — C. B. Leovy
153
I'ii^^m
r
W'
%.
id
4
/t<^
• *'
/n
^<y
:JA
U4AL
V^-^tf-.V"
■',■ • \ ■
/ » .
(48°N, 40°W)
Clouds appearing on three successive days along the .southern edge of the north polar
hood reveal a prevailing large-scale wind pattern (repeated craters indicated by cor-
responding arrows). Intensely cold air covers the northern part of the region shown.
Some of the wave clouds on the second day of this sequence were aligned in parallel
bands, southwest to northeast, and individual elements were perpendicular to the band.
This structure suggests waves produced in shearing flow along the bands and perpen-
dicular to the small wavelets. This type of structure is familiar in terrestrfal satellite
photographs of cold fronts and their associated jet streams. On the third day, the
band system had moved 1000 km to the southeast. This movement is typical for terres-
trial cold fronts, and martian cold fronts appear to behave similarly. — C. B. Leovy
'^f/t
W«^
w^
— .-^
i^^
M
(71°N, 351°W; IPL 7283/213013)
Mariner 9 sent back some pictures in the northern spring when the polar hood had
cleared and the atmosphere there was generally very clear. Later photographs (one
shown at right) showed that the atmosphere was again partially obscured north of about
45° latitude. Well defined cloud streaks extended south and west from the edge of the
surface condensate cap. The streakiness may have been produced by strong winds
blowing off the edge of the subliming polar cap, but this phenomenon is still poorly
understood. — C. B. Leovy
(8°S, 95°W; IPL 0083/151448)
The equatorial region around Tharsis Monies shows a general dust pall in this early
photo. The peaks of towering volcanoes appear as dark rings at the left, and at right
the bright outline of a vast canyon complex, later identified as the west end of Valles
Marineris, can be seen. Observations showed that the canyons are several kilometers
deep and the brightening here is attributed to the depth of the dust scattering back the
Sun's light to Mariner 9's cameras. — G. A. Briggs
156
v?v<#»
,: » : V :'
Wmsi^
x;4^^
'* <*,''i^'<*"' ■ ■■■■ - ■ ■ .-
■:';>y?:
;^-;%
■,^i
'>
(45°N, 85°W)
(55°N, 73°W; MTVS 4154^93)
(43°N, 82° W; MTVS 4229-66)
The Mariner 7 photo at far left shows a white cloud in the Tempe region (arrow) that
astronomers have noted there for many decades. Mariner 9 returned better views in
1972 showing parallel corridors of clouds that ranged up to about 30 km in altitude
(above, left). When viewed vertically later, it was found that a surface ridge about
400 km long (above, right), oriented roughly north-south, caused the cloud waves.
Their composition is probably dependent on the wind velocity. Strong winds produce
oscillations that permit CO2 to condense at high altitudes and water vapor at low,
warmer elevations. Weak winds permit only the lower level condensation of water
vapor into ice crystals. — G. A. Briggs
159
(63°N, 347°W; MTVS 4210-78)
This high resolution photograph shows details of the formation of a wave cloud over
a crater in the north polar region. The wind is blowing from upper right to lower left,
and a second wave cloud is forming about 40 km downstream. Both wave clouds
appear to be quite turbulent. The generally diffuse appearance of the scene is caused
by partial obscuration by a widespread thin haze of condensed CO2 or H2O. The large
crater stands out prominently because of surface ice or snow (CO2 or H2O) around
its rim. — G. A. Briggs
160
14
Natural Satellites
The tiny martian moons Phobos and Deimos ( from
the Greek for "Fear and Dread") are very difficult to see
with terrestrial telescopes. They were discovered only in
1877 by the American astronomer Asaph Hall, and were
seen as faint points of light orbiting close to their planet.
Virtually nothing was known about them until Mariner 9
returned the images shown here. Because their orbital
characteristics were not known with sufficient precision,
the first photographs were taken at substantial distances.
These images were then used for accurate orbital deter-
minations, which permitted accurate camera aiming for
closeup photography.
Phobos, the inner and larger of the martian moon-
lets, orbits at an average distance of 6100 km (3750
miles I above the surface of Mars. It proves to be an
oblong mass about 20 by 25 km in its major dimensions
(12 by 14 miles). Deimos orbits roughly 20 000 km
(12 000 miles) above Mars, and is 10 by 16 km (6 by 10
miles) in size. Because the martian moons are so small,
their gravity fields are too weak to force them into
spherical shape. As with our Moon, each keeps the same
side turned toward the planet.
Both Phobos and Deimos are heavily cratered by the
impact of meteoroids. The number of craters appears to
be close to the saturation limit, which occurs when so
many exist on a surface that any new craters formed de-
stroy an equal number of older ones. Rough estimates of
the ages of satellites can be made by comparing their
crater densities with those of similar areas on the Earth's
Moon that have been positively dated by the ages of rocks
returned by Apollo astronauts. Phobos and Deimos are
believed to be at least 2 billion years old, and may date
back to the early history of the solar system about
4.5 billion years ago. The satellites also serve as a useful
standard of comparison for the crater densities on Mars.
This comparison suggests extensive erosion of craters
1 km in diameter and smaller.
Both Phobos and Deimos are dark objects; most
asteroids and meteorites are brighter. The few objects
that are as dark contain large amounts of carbon or iron.
Studies of variation in brightness of these satellites
suggest that they may be covered with a layer of fine
particles. In the case of the Earth's Moon, such a regolith
results from the shattering of rocks by repeated mete-
oroid impact. The gravity fields of Phobos and Deimos
are so slight that fragments of impact-shattered rock
would be thrown out into space. But these ejecta would be
captured by the gravity field of Mars, going into orbit
about Mars where the weak gravity of each satellite could
sweep it up again.
Theoretical studies of the small satellites indicate that
they need rocklike strength to escape total disintegration
from meteoroid impact. Since their weak gravity appears
insufficient to have originally formed them into cohesive
materials of sufficient strength, it seems likely that they
were once part of a much larger solid rock, and were
fragmented by the impact of a large meteoroid. —
J. B. Pollack
163
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(IPL 1579/163600)
Phobos from afar at a range of 12 500 km (left) reveals only its largest craters. The
diameter of the prominent crater near the terminator is about 5 km. The long linear
edge that runs the length of Phobos is probably the result of fragmentation. — J.
Veverka
(IPL 83/235451)
The best view yet seen by man of Phobos is this computer-enhanced picture taken at a
range of 5540 km ( right ) . The large crater at middle right, near the terminator,
appears to have at least one small crater on its rim. More than a dozen other small
craters are visible. The irregular edges of Phobos strongly suggest fragmentation.
—J. B. Pollack
165
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(MTVS 4109-9)
The profusion of craters on Phobos is suggested in this picture, which is also a mini-
mum-range view (5760 km). Craters as small as 300 m in diameter are visible.-J.
Veverka
lii ', I'
tt
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(IPL 1599/200513)
Deimos, photographed at a range of 5465 km, reveals less detail, although craters of
all stages of freshness are seen. The old crater in the center is about 2 km across.
— J. Veverka
15
Martian Enigmas
Many of the martian features seen in Mariner 9 pic-
tures can be categorized because of their obvious similar-
ity to features well known and long studied on the Earth
and the Moon. Others, however, are puzzling. We cannot
yet be sure whether their characteristics are unique to
Mars, or whether it is just that the limitations on our
current understanding of the red planet prevent us from
confidently interpreting what we see.
More detailed study will doubtless lead to a better
understanding. Some features may be clarified if we
can find natural features on Earth that are analogous,
and others may be explained if they can be simulated
or modeled in a laboratory. Thus the present enigmas
may lead us to a better understanding of the processes
that operate on the cold, dry surface of Mars with its
very thin atmosphere and periodic high winds. In the
meantime, a modest and by no means exhaustive collec-
tion of these puzzling features is presented here as a
sampling of the challenges that have been presented by
Mars. — J. E. Peterson
169
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A strange white deposit occurs on the floor of a crater not far from the martian
equator. Its high reflectivity suggests ground ice but its location makes this highly
improbable. The deep tapering reentrants and the suggestion of considerable relief
above the crater floor leads to the inference that it most probably is not a transient
feature but rather a permanent deposit nov^ in the process of being eroded by the
wind. The origin of the deposit itself, which is about 18 km wide, remains an enigma.
—J. F. McCauley
(74°S, 166°W; MTVS 4269-19)
An intricate crater (above) in the south polar region displays an arcuate slump mass inside
the major crater wall. Both the rim and the slump mass are subdued by a mantling; blanket.
On the crater floor an arcuate scarp appears, which is 35 to 40 km in diameter and compa-
rable in shape to the big crater. Branching ridges and furrows within may be due to erosion
of a volcanic construct; dark pattern within may be volcanic ash. — D. B. Potter
(80°S, 245°W; IPL 326/171411)
A complex pattern of delicate swirls and irregular dark tones shows in this picture of
unusual terrain in Mars' south polar cap. The area covered is about 80 by 85 km. Puzzling
processes, perhaps some interplay of wind deflation of layered terrain, have modified the
terrain. — L. A. Soderblom
173
(2°S, 186°W; MTVS 4209-75)
Wrinkles on the face of Mars: The smooth plains are sometimes marked by incipient
collapse or flowage. It may be analogous to the landslips that occur in silty clay beds
in the St. Lawrence Valley in Quebec. Collapse might come from displacement of sub-
surface fluids, or from melting of a permafrost layer. Here collapse occurs on the
flanks of a low ridge that extends from lower right to upper left. — E. C. Morris
(67°S, 188°W; IPL 1436/130925)
Double impact craters (below), with rims and floors thinly mantled, boast striking
breached volcanic cones rising from each floor. Each cone is surrounded by a dark
apron that could be lava or volcanic ash. — D. B. Potter
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(65°S, 325°W; IPL 7225/14336, 1671/223240)
Variable features, pictured twenty days apart, offer a challenge to our understanding.
View at left was acquired on February 4; one at right on February 24. Differences in
light areas are probably caused in part by clouds. The changes in irregular patches of
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extremely dark material may be caused by settling of dust on dark, fresh lava flows.
Nearly all the craters in these pictures have a central peak or dome, some capped by
small craters, which is very suggestive of volcanism. — J. E. Peterson
''mmw'
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(54°S. 179°W; IPL 1406/225906)
The "peach pit" (above, left) : the dark interior mound within this crater is of inde-
terminate origin. The light materials in and around the crater are probably wind-
blown sediment. — T. A. Mutch
(38°S, 120°W; IPL 7081/154812)
This flat-topped mountain (above, right), about 20 km across, stands more than 1
km above undulating plains in the southern hemisphere. Steep sculptured slopes indi-
cate erosional processes are causing escarpment retreat. A complex ring-like structure
encircles the mountain and resembles a graben — a downdropped trough — along the
left and top sides but becomes indistinct at right and bottom of the image. A low
ridge runs from the center of the flat top to the lower right beyond the ring, while a
fault scarp crosses the mountain and ring structure from left to right. This large
mountain is of unknown origin, and does not resemble terrestrial volcanic-ring or
impact features. It somewhat resembles large outliers of chaotic terrain found more
than 2000 km to the east on Mars. — H. E. Holt
t35°S, 216° W; MTVS 4248-31)
Twin volcanic ranges about 20 km long have some unusual features. Tiny craters cap
the peaks in each range (arrows). The southwest slope of the southwest range has an
escarpment furrowed by small channels. The other slopes show mass wasting and lobes
of slide material. The ranges lie within a very large crater not shown here. — J. W.
Allingham
179
(43°S, 356°W; MTVS 4149-15)
Three unique features lie in the low resolution area shown below. They are large
crater-like depressions of unknown origin. Being closed forms, they cannot have been
caused by fluvial erosion, and their depth and steepness of sides rules out wind erosion
as the sole cause. Some mechanism of collapse controlled by fracture systems is prob-
ably responsible, but these features are still very puzzling. — J. E. Peterson
(49°S, 358°W; IPL 7205/184628)
Curving within a 100-km crater is a 60-km long depression, the end of which is shown
here (right, top) . Its walls are very steep, and there appears to be a flat-lying resistant
layer at its rim. It is about 7 km wide at the arrows. Clouds partly obscure the pic-
ture.— J. E. Peterson
(45°S, 356°W; IPL 1943/201557)
A central plateau in this unique 85-km diameter feature is connected to the surround-
ing plains (right, center). The steep-walled depressions are somewhat sinuous but
follow a roughly circular outline. This picture was acquired near the end of the
global dust storm and is somewhat obscured. — J. E. Peterson
(50°S, 357°W; IPL 7455/235030)
A deep linear depression is terminated (right, bottom). It is about 5 km wide at its
narrowest point. The sides are very steep, with debris-avalanche chutes on the walls,
but the bottom seems fairly smooth and rounded in cross section. Again, clouds
apparently obscure this picture somewhat. This gash extends nearly across a large
crater. — J. E. Peterson
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(20°N, 235°W; IPL 1765/212715)
(18°N, 235°W; IPL 7256/131906, 7256/133526)
This strange feature (above), Hephaestius Fossae, is located in the Elysium Planitia.
It is a system of branching troughs approximately 525 km long and 75 km wide. The
elongate shadow of Mars' moon Phobos can be seen in the low resolution photo (the
round black spot is a camera artifact). In the high resolution mosaic, the general pat-
tern of the troughs indicates fracturing as a more likely cause than fluid flow. Indi-
vidual troughs are up to 2 km wide, and considerable erosion by wind may have
broadened them. — R. S. Saunders
(9°N, 293°W; MTVS 4266-35)
An enigmatic collapsed depression (left) occurs in the region of Syrtis Major Planitia.
The structure here has the crisp arcuate scarps that characterize the volcanic calderas
of the Tharsis Montes. But it may also be a karst-like feature formed by removal of
deeply buried ice or other subsurface materials. (A karst is a region of sinks and
ridges overlying limestone.) — T. A. Mutch
183
16
Similarities:
Mars, Earth, and Moon
It is impossible to look through the thousands of
images of Mars returned by Mariner 9 without discover-
ing features reminiscent of those on our native planet.
When a match-up is made by geologists having profes-
sional familiarity with the Earth's features, as on the
following pages, the similarities can be striking. The
Moon, liberally photographed during the first years of
space exploration, also has details that appear similar to
those that Mariner 9 revealed on Mars. Sometimes labo-
ratory simulations can help bridge the gap between the
apparent and the known, as when wind-tunnel experi-
ments on model craters seemingly duplicate erosion pat-
terns seen on the surface of Mars.
For two reasons these analogs may be less surprising
or significant than they seem. In a sense it is small wonder
that Mars, Earth, and Moon do, in fact, look somewhat
alike, particularly if you examine the Earth through
geologists' eyes. Windblown features are easily identifi-
able in, for example, Texas. Idaho, and New Mexico.
Evidence of volcanism can be seen in Arizona, faulting
in California, stream erosion throughout the United
States, stratified deposits in Utah, and glacial features in
Alaska. The Hawaiian Island complex is comparable in
some respects to the volcanic region of Mars near Olym-
pus Mons.
We should be cautious and not make the mistake of
assuming that resemblances — limited as thev are to the
physical appearance of surface features — are proof of
true similarities. It can be a profound mistake to assume
that similar-looking features actually originated and
evolved in a like manner. Without a doubt, future ex-
ploration of Mars will show that some of the dynamic
processes that shaped the surface of Mars were the same
as those that caused terrestrial features. Geologists are
now conducting research programs in the southwestern
United States, Peru, and Antarctica to collect data that
may cast light on the question of whether Mars and
Earth evolved similarly. Theoretical calculations and
laboratory experimentation will provide the quantitative
information needed to understand the physics of these
processes.
The exciting thing about comparative planetology is
that it will permit us to unfold the lost part of the
Earth's history, now largely obliterated by erosion, moun-
tain building, and other processes. A full understanding
of the past is a reliable way to accurate prediction of the
future. This work can help predict the nature and course
of future atmospheric evolution, answering the disturbing
question of whether the Earth's environment is destined
to grow similar to the environment of Venus or Mars.
Questions like these can only be approached by compre-
hending the secrets of the planets in our solar system.
Comparative planetology is the starting point for an
understanding of the physical future of planet Earth.
In the meantime, the analogs on the following pages
suggest that the old saying may have to be modified to
■'It's a small solar system." — S. E. Dwornik
185
(14°N, 142°W; MTVS 4174-75)
Wind-produced streamlining of a part of the complexly structured aureole around Olympus
Mens is seen above. These elongate ridges are 10 to 15 km long and 3 to 5 km wide. They
are parallel to numerous smaller grooves and roughly elliptical pits that are also the probable
result of wind erosion. The crests of many of these ridges occur sharp and keel-like in appear-
ance; their ends are sharply tapered. These ridges occur in terrestrial deserts such as Iqa
Valley in Peru (right) where they are several kilometers in length and hundreds of meters
high. The Iqa Valley ridges have been cut by strong sea winds that funnel almost daily into
this virtually rainless valley. The layered rocks here are relatively soft. Tertiary sediments
uplifted from the sea by faulting since the onset of aridity in this region. — J. F. McCauley
186
J
.-^f^m-i^r
187
(81°S, 64°W; IPL 1417/160341 1
Another probable result of wind erosion (below ) is seen in this unusual and complex
array of linear, interconnected reticulate ridges in the south polar region of Mars.
(The picture is about 45 km wide.) A superficial resemblance to ancient ruins led to
their informal appellation as "Inca City" during the Mariner 9 mission. A more mun-
dane explanation is that this feature almost surely represents yet another variant of
the landforms produced by wind on Mars. The origin of the reticulate pattern itself
is unknown; igneous or clastic dikes or indurated fracture zones are all possibilities.
As can be seen in the photo from the almost rainless coastal desert of Peru (right),
similar patterns can be produced by selective wind scouring. (The image is about 21/^
km across. I The more resistant dikes or fractures abrade less rapidly than the softer
surrounding material and thus stand above the surrounding plains like the walls of a
ruined city. — J. F. McCauley
^.
c<^^
'i*/
190
(18°N, 133°W; IPL 1406/164237)
Calderas on Earth are created by the collapse of the surface as lava is erupted or when
it drains away at depth. Here repeated collapse events produced complexes of older
large calderas surrounding a smaller younger one. Shown are Kilauea in Hawaii
(above) and Olympus Mons (left) on Mars.— K. A. Howard
191
1
1
B
1
Wliit'
(1°N, 157°W; MTVS 4254^55)
U-shaped depressions are often produced by the wind in the lee of rocks or other
topographic obstacles. These occur where an active, mobile sheet of loose-moving sand
is present on the surface. Deposition of the sand tends to occur on the upwind side and
the flanks of the obstacle and an erosional blowout or depression occurs on the down-
wind side. These features may be controlled in great part by the presence of partially
buried crater rims just now poking above the sand blanket. Picture at left is a high
resolution image of the Amazonis Planitia on Mars; blowouts shown are up to 3 km
long. The picture above is a low-altitude aerial photo taken in the Coachella Valley,
California, where the blowouts are tens of meters long and occur in the lees of
abandoned shacks. — J. F. McCauley
193
(6°S, 84°W; IPL 1356/114237)
Stubby, relatively deep gullies without well developed tributaries are seen in the photo at
right of an alluvial wash on the shore of Lake Mead, Arizona. They are developed in
loosely consolidated material that fails by slumping and soil flowage due to changes in
the lake level and degree of saturation of the soil. A similar stubby, poorly developed
dendritic pattern (above) is seen in many tributaries of the Valles Marineris on Mars,
suggesting that they may have formed by some type of sapping or soil ffowage process
rather than by water collected runoff from rainfall during an earlier pluvial episode on
Mars. — J. F. McCauley
194
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(2°N, 314°W; MTVS 4178-60
Central peaks in craters or basins, though widely assumed to have been formed by
impact or volcanic processes, can also arise from wind deposition. While the origin of
the peak in the Mars crater (left) is as yet unproven, in the basin shown above at
Bruneau, Idaho, the center is dominated by a large sand-dune complex maintained by
wind blowing in two main directions. — J. D. Murphy, J. S. King, and R. Greeley
197
(56°N, 16°W; IPL 1643/194728)
Clouds on Mars can resemble those on Earth. Flowing past a frost-rimmed crater 90 km
in diameter, northern winter winds form clouds of a characteristic lee-wave pattern
on Mars (below). At right, a similar lee-wave pattern was seen by Nimbus 1 down-
stream of the Andes over Argentina. — C. B. Leovy
f '^f%
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(60°N,270°W; IPL 1431/193738)
(60°N, 178°W; MTVS 4248-98)
Long cloud lines on Mars (left, top) are formed by convection as cold polar at-
mosphere rushes southward over warmer ground. The convection creates long spiral-
ing plumes downwind, with clouds forming on the rising part of the spiral. At left
bottom, similar cloud lines begin to break up into large convective clusters in another
part of the martian north polar region. Above, an Apollo photo shows cloud lines on
Earth, where relatively cool air from the Atlantic flows northward over the warm
ground of South Carolina. — C. B. Leovy
201
•^
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f ¥
«r'
nm
(25°N, 213° W; MTVS 4298-40)
Radial structures about this summit caldera in the Elysium Planitia of Mars (left) are
interpreted as fractures that have been modified by lava flows. Compare them with
the similar fracture from the rim of the Mauna Loa caldera, pictured above. (A small
segment of the caldera rim is in the upper part of the picture. ) — R. Greeley
203
(38°N, 196° W; MTVS 4244-76)
Martian inselbergs near Phlegra Monies (left) and terrestrial inselbergs in New
Mexico (below). In dry climates these eroded remnants of mountains are sometimes
surrounded by bajadas (debris sheets). A good example is seen in the upper right of
the Mars photo. Most terrestrial mountains are eroded gradually and smoothly both
by wind and rain; debris is washed evenly onto the surrounding area. However, in
deserts infrequent but voluminous cloudbursts are responsible for the transport of
great quantities of rock materials that accumulate as a depositional apron around the
inselberg in Animas Valley, New Mexico. Bajada-like features are also seen on Mars;
their origin is uncertain since there is no present fluvial activity. Perhaps these debris
aprons are related to the desiccation that is evident from dry stream channels. The
bajadas also may have formed simply by gravity as the debris slid down the slope to
flat areas. The terrestrial inselbergs shown here are approximately 1 km in diameter:
the remnant in the upper right of the Mars photo is about 10 km in diameter including
the bajada. — W. E. Elston
^-:^^KfX^ "-(*•
205
(9°N, 191°W; IPL 1947/173205)
A dark plume (left I extends more than 140 km downwind of this large crater in the
Elysium Planitia. A laboratory simulation above, with the wind flowing from top to
bottom, suggests that the dark martian plume may have been caused by wind erosion
removing loose particulate material. Alternatively, the dark plume may be deposits of
material originating from within the crater. — R. Greeley
Zi
0
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'- VT' ■ j ^>'' ■
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Wind-tunnel simulation examines effects of low-velocity wind flowing (left to right)
past a raised-rim crater. Note the development of the blowout on the downwind flank
of the crater. Such tests must consider wind velocity, crater geometry, threshold char-
acteristics of surface material, scaling effects of size of crater, and effects of martian
environment. — R. Greeley
209
(16°N, 182°W)
Very large, irregularly shaped craters exist on Mars (above) and on the Moon (right).
The martian crater, Orcus Patera, is more than 400 km long; the lunar crater,
Schiller, is about 180 km long. Craters of this shape and size are uncommon and their
origins uncertain. Coalescing subcircular segments marked A suggest they may have
been formed by overlapping impacts or as volcanic features, but linear scarps and
troughs marked B indicate a tectonic influence. Floors of both craters are flat and
smooth. The martian crater is probably floored with wind-blown dust; the floor of
Schiller may be covered by impact ejecta and volcanic flows. — D. H. Scott
(31°N, 220°W; IPL 1443/140643)
Highly elliptical craters on Mars and the Moon. Note that both the 12-km-long Messier
A lunar crater (right, bottom) and the 15-km-long unnamed martian crater (below)
have raised rims, linear structure on their floors, and ridge-like topography outside the
long axis of the ellipse. While certain of these features have been interpreted as evi-
dence for volcanic origin, laboratory studies have shown that the observed features
can be reproduced in detail by low-angle meteorite impact. — N. W. Hinners
f^mf-^-'^^J'^m-n^.
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(13°N, 107°W; MTVS 4184-75)
Interrupted rilles appear both on Mars (left) and on the Moon. In each case low-ele-
vation terrain adjoins high-elevation terrain, and both are transected in varying degree
by rilles. Some of the martian rilles, such as those near the sinuous channel at upper
left, may have been filled by deposition or sediment. Parts of the lunar rilles seem
to have been somewhat filled by later lavas. Scale: the middle martian rille has an
average width of 700 m; the largest lunar rille shown is about 2 km wide. — N. W.
Hinners
215
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i (23°S,204°W; IPL 1642/1883351)
Heavily cratered terrain on Mars (above) bears striking resemblance to some areas on
the Moon (right). One notable difference is that Mars does not appear to have as
many smaller, bowl-shaped craters, which leads to the inference that, on Mars, they
may have been eroded and filled. — N. W. Hinners
^* vn
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(Altxid* ^~ - t
(31°N, 192°W; IPL 1449/223730)
Similar valleys on different worlds: a martian valley near Phlegra Monies (below) and
Alpine Valley on the Moon (right). Both cut plateaus are studded with rugged peaks
and the valley floors are filled by smooth plains materials. The Alpine Valley, 130 km
long in the photo, belongs to a radial fault system in the Imbrium basin rim; the
plains materials are post-basin mare basalts. The martian valley (photo width is 55
km) could also be a fault graben, but no relation to a basin has been discovered, and
its origins are uncertain. — D. E. WilheLms
i^^-^'-J
■^N >■
Availability
of Photographic Prints
Throughout this publication Mars imagery is identi- Information and price lists for general interest re-
fied by MTVS or IPL numbers except where mosaics are quests for any photo in this publication may be obtained
presented. These numbers represent the best processed from
image available. d du » u;„ i
'^ ri r 1 i_ c f Bara Photographic, Inc.
NSSDC has Mars photos on file for the benefit of p ^jr- r. 4^05
scientists engaged in the study of Mars. Inquiries (for Bladensbur", MD 20710
MTVS or IPL numbers only) should be directed to
National Space Science Data Center Orders should include the publication number (NASA
Goddard Space Flight Center SP-329) and the page number (indicate "top" or "bot-
Code 601 tom" where necessary).
Greenbelt. MD 20771
221
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Polar Stereographic Projection
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NORTH POLAR REGION
POLAR CAP AS IT APPEARED ON OCTOBER 12, 1972
222
Shaded Relief Map of Mars
SOUTH POLAR REGION
POLAR CAP AS IT APPEARED ON FEBRUARY 28, 1972
180
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Mercator Projection
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MM^:M:^i
DATE DUE
Vtld^
PRINTED INU S*
HElUSLEy COLLEGE LIBRARY
3 5002 03009 073 7
qQB 641 . W36
Mars as viewed by Mariner 9 ^
030Cfi 073 1 _
I
qQB 641 . M36
Mars as
viewed by Mariner 9
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