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Full text of "Concepts for detection of extraterrestrial life"

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NASA SP-56 



CONCEPTS FOR 
DETECTION OF 
EXTRATERRESTRIAL LIFE 




NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 



CONCEPTS FOR DETECTION OF 
EXTRATERRESTRIAL LIFE 




Photograph of Mars obtained on August 24, 1956 (18 days before the opposition 
on September 11, 1956) by R. B. Leighton of the Cahfornia Institute of Technology. 
The distance between Earth and Mars at the time the photograph was taken was 
about 35,000,000 miles. The Mt. Wilson 60-inch reflector was used with its aper- 
ture cut to 21 inches by an oflF-axis diaphragm. The exposure time, on Kodachrome 
Type A film, was 20 seconds. The positive, used in making the print, was composed 
by George Emmerson at the Jet Propulsion Laboratory. 

This color photograph suggests that the darker areas of Mars are not necessarily 
"green" in color as they are often described, but may be a darker shade of the 
prevailing yellow-orange light areas. It is noted that the photograph as it appears 
here has been subjected to duplication in the course of which some minor color 
changes occurred. The brilliant white south polar cap is clearly evident. Rather 
surprisingly, this cap is probably just what it looks like — a thin layer of frozen 
water, perhaps in the form of hoarfrost. As the polar cap recedes, the dark areas 
(especially those in the same hemisphere) become darker. The dark area near the 
lower right-hand limb of Mars is Syrtis Major, one of the most prominent and well- 
known features of the planet. This feature, among others of its kind, has been 
of increasing interest to exobiologists in recent years. The extremely light-colored 
area to the right and just below the ice cap is Hellas, one of the most prominent 
Martian desert areas. 



NASA SP-56 



CONCEPTS FOR 
DETECTION OF 
EXTRATERRESTRIAL LIFE 



Edited by 

Dr. Freeman H. Ouimby 

Office of 
Space Science 
and Applications 




Scientific and Technical Information Division 1964 

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 

Washington, B.C. 



Acknowledgments 



The editor wishes to express his appreciation for special technical and edi- 
torial assistance to: Dr. Klaus Biemann, Massachusetts Institute of Tech- 
nology; Dr. Ira Blei, Melpar, Incorporated; Dr. Carl Bruch, National 
Aeronautics and Space Administration; George Hobby, Jet Propulsion Labora- 
tory; Dr. Norman H. Horowitz, California Institute of Technology; 
Dr. Thomas Jukes, University of California; Dr. Elliott Levinthal, Stanford 
University Medical Center; Dr. Sol Nelson, Melpar, Incorporated; Dr. Carl 
Sagan, Smithsonian Astrophysical Observatory and Harvard College Observa- 
tory; Dr. Gerald Soffen, Jet Propulsion Laboratory; Dr. Wolf Vishniac, 
University of Rochester; and Dr. Robert Kay, Philco Research Laboratories. 

The entire text has been reviewed by Drs. Horowitz and Sagan. 

F.H.Q. 



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FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE, 

WASHINGTON, D.C., 20402 — PRICE 50 CENTS 



Preface 



The principal objective of tlie search for life on another celestial bodj^ is 
to determine the state of chemical evolution if life has not yet arisen, or the 
state of biological evolution if life is present. A study of such life might con- 
tribute to a universal concept of the origin and nature of living systems. 
In addition, chemical and microscopic examination of any fossils from a pre- 
existing biota could provide equally valuable information. 

This subject has provoked excessive speculation by some scientists, while 
others seem unaware of the implications of seriously confronting it. The quest 
for life in space rests on a reasonable degree of geological plausibility. A widely 
accepted theory argues that the known planets condensed under conditions 
compatible with the retention of water, ammonia and methane as gases in the 
primitive atmospheres. Laboratory experiments have demonstrated that 
primeval energy sources would have synthesized numerous biologically- 
significant molecules from these gases. Life developed on Earth when these 
gases and energies were also available to the other planets. Furthermore, 
it is both factual and perplexing that (except for helium) there is a closer 
resemblance between the elemental composition of living systems and the 
universe than there is between that of living systems and the rocky material 
in the terrestrial crust on and in which such systems are in intimate residence. 
Indeed, living matter on Earth displays a "unity of biochemistry" which may 
well be a principle with cosmic as well as terrestrial validity. 

These arguments do not prove the hypothesis, but suggest that we cannot 
avoid the experiment. It is the purpose of this publication to describe briefly 
this experiment for the academic community and the public. Some of 
the methods which have been considered thus far for the detection of extra- 
terrestrial life and life-related substances in the near reaches of space are 
presented. 

Homer E. Newell, 
Associate Administrator for 
Space Science and Applications 



Contents 

CHAPTER PAGE 

Introduction 1 

I. Evidence Relevant to Life on Mars 7 

II. Mars Surface High-Resolution Near-Scan TV 11 

III. The Vidicon Microscopes 13 

IV. The Gas Chromatograph 17 

V. The Mass Spectrometer 21 

VI . The Ultraviolet Spectrophotometer 23 

VII. The J-Band Life Detector 27 

VIII. Optical Rotation 31 

IX. The Radioisotope Biochemical Probe: Gulliver .... 35 

X. The Wolf Trap 39 

XL The Multivator Life-Detection System 45 

XII. The Mars Mariners and Voyagers 49 

Bibliography 51 

Suggested Reading 53 



vu 



Introduction 



The mystery of his own origin has intrigued man since earHest antiquity. 
Throughout the ages he has puzzled and theorized over the question of how 
he began, where and when. 

But man is hke a detective arriving at the scene some millions or billions of 
years after the event and trying to reconstruct the event. The principals have 
long since departed; most of the clues have disappeared; even the scene itself 
has changed. 

Of equal fascination today is the question of life on other worlds — extra- 
terrestrial life. Do the seasonal changes in the darkening on the Martian sur- 
face mean that plant life blooms, withers, and dies there.'' Are there living 
things beneath the covering clouds of Venus despite the great heat this planet 
is subjected to.? Did life on the Moon go underground eons back when the 
atmosphere departed; and does life, or its residue, still exist there.? Is Jupiter 
actually ice encrusted beneath its hydrogen shroud; and if it is, does this 
preclude some form of life undreamed of by man.? 

Now, for the first time, man is beginning to grasp the key which may solve 
the question of whether or not life in some form exists on the other celestial 
bodies of our solar system. The key is, of course, the technology of space 
exploration. The search for life in space now being planned by the National 
Aeronautics and Space Administration is part of that technology. 

The question of extraterrestrial life and the question of the origin of life are 
interwoven. Discovery of the first may very well unlock the riddle of the 
second. 

The oldest form of fossil known today is that of a microscopic plant similar 
in form to common algae found in ponds and lakes. Scientists know that 
organisms like it flourished in the ancient seas over 2 billion years ago. (See 
fig. 1.) However, since algae are a relatively complex form of life, it is obvious 



I DETECTION OF EXTRATERRESTRIAL LIFE 

that life in some simpler form originated much earher. Organic material 
similar to that found in modern organisms can be detected in these ancient 
deposits as well as in much older Precambrian rocks. 




XI 500 




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INTRODUCTION 




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Figure 1. — Representative microfossils, three-dimensionally preserved in chert from the 
Gunflint iron-formation of the north shore of Lake Superior. This formation is of middle 
Precambrian age and has been dated by K*° -Ar*° as approximately 2 X 10' years. All 
figures are from thin sections of the chert photographed in transmitted light. Published 
here for the first time (from Dr. E. S. Barghoorn). 



^ DETECTION OF EXTRATERRESTRIAL LIFE 

By studying the radioactive decay of minerals, scientists have determined 
that the surface of the Earth hardened into something hke its present form 
about 4.5 to 5 billion years ago. Life itself probably arose during the first 
billion years of the Earth's history. 

Although the planets now have differing atmospheres, it is believed that in 
their early stages the atmospheres of all the planets may have been essentially 
the same. 

The most widely held theory of the origin of the solar system states that the 
planets were formed from vast clouds of material containing the elements 
in their "cosmic" distribution. Among the most abundant elements in our 
galaxy are hydrogen, oxygen, nitrogen, and carbon. These were present in 
the primitive atmosphere of the early Earth in the form of water, ammonia, 
methane, and hydrogen. Later, this reducing primitive atmosphere was 
altered to our present oxidizing atmosphere by the escape of hydrogen and 
by the formation of oxygen through the photodissociation of water vapor 
in the upper atmosphere and through plant photosynthesis. The Earth's 
present atmosphere consists of nitrogen and oxygen in addition to relatively 
small amounts of other gases; most of the oxygen is of biological origin. 
Some of the atmospheric gases, in spite of their low amounts, are crucial 
for life. The ultraviolet absorbing ozone in the upper atmosphere and carbon 
dioxide are examples of such gases. 

On other celestial bodies different things happened to the atmospheres. 
The Moon with feeble gravitational attraction was unable to retain any 
atmosphere at all. Jupiter and Saturn, large in size and with a much more 
powerful gravitation and cooler atmospheres, retain hydrogen, hydrogen 
compounds, and helium. 

Scientists believe that the synthesis of organic compounds preceding the 
origin of life on Earth occurred before its atmosphere was transformed from 
hydrogen and hydrides to oxygen and nitrogen, supporting their theory by 
laboratory experiments. In these experiments, a mixture of gases similar to 
the primitive atmosphere is prepared and energy is applied; i.e., energy in 
the form of an electric spark or ultraviolet light. These and other forms of 
energy were available on the primitive Earth. 

By this action, simple organic molecules are formed. This is not to say 
that the molecules are alive, although they are constitutents of living things 
on Earth. 

Among these molecules are the building blocks of proteins (amino acids) 
and the building blocks of DNA. The latter is the genetic material which 
contains information for the development of the individual organism and which 
is passed from generation to generation. 



INTRODUCTION i 

Scientists, in fact, can duplicate many of the individual steps through which 
they think life first arose. But they cannot (or cannot yet) reconstruct the 
actual process by which life originated, a process which may have occupied 
Nature for hundreds of millions of years. 

At some point energy and chemical materials combined under the right 
conditions and life began. Nucleic acid molecules were probably formed as 
well as other complex molecules which enabled the nucleic acids to replicate. 
Due to errors in replication, or mutations, evolution occurred, and in time many 
different life forms arose. Since this happened on Earth, it is possible that 
it also happened on other planets. 

The NASA program of space exploration for the next few decades holds 
great promise of solving one, and of throwing light on the other, of these 
great twin mysteries — extraterrestrial life and the origin of life. American 
space technology is now developing the capability of exploring the Moon 
and the planets of our solar system to search there for organic matter and 
living organisms. 

Spacecraft have flown past, and crashed on, the Moon. Mariner II, launched 
from Cape Kennedy on August 27, 1962, flew past Venus on December 14, 
1962, taking readings and transmitting data which are significant in the 
search for extraterrestrial life. Mariner's measurements showed temperatures 
on the surface of Venus in the order of 800° F, too hot for life as known on 
Earth. 

Other flights past Venus and to Mars are planned. Later, Instruments will 
be sent to Mars in search of extraterrestrial life or biologically significant 
molecules. Culture media, microscopes, and chemical detecting devices will 
search out micro-organisms and life-related substances. Eventually, tele- 
vision cameras will look for foliage — and, who knows, footprints.'' 



CHAPTER I 



Evidence Relevant to Life on Mars 

BY Dr. Carl Sagan 



The difficulty of directly detecting Martian life can be easily understood 
if you imagine yourself on Mars, peering through a large telescope at Earth. 
Detecting life on Earth — particularly intelligent life — from such a vantage 
point would be extremely difficult. In view of this, it is not surprising that the 
question of life on Mars is as yet unresolved. In general, there are three 
approaches which can be taken to this problem. 

The Origin of Life 

In the past decade, considerable advances have been made in our knowledge 
of the probable processes leading to the origin of life on Earth. A succession 
of laboratory experiments has shown that essentially all the organic building 
blocks of contemporary terrestrial organisms can be synthesized by supplying 
energy to a mixture of the hydrogen-rich gases of the primitive terrestrial 
atmosphere. It now seems likely that the laboratory synthesis of a self- 
replicating molecular system is only a short time away from realization. The 
syntheses of similar systems in the primitive terrestrial oceans must have 
occurred — collections of molecules which were so constructed that, by the 
laws of physics and chemistry, they forced the production of identical copies 
of themselves out of the building blocks in the surrounding medium. Such a 
system satisfies many of the criteria for Darwinian natural selection, and the 
long evolutionary path from molecule to advanced organism can then be under- 
stood. Since nothing except very general primitive atmospheric conditions 
and energy sources are required for such syntheses, it is possible that similar 
events occurred in the early history of Mars and that life may have come into 
being on that planet several billions of years ago. Its subsequent evolution, 



8 



DETECTION OF EXTRATERRESTRIAL LIFE 



in response to the changing Martian environment, would have produced 
organisms quite different from those which now inhabit Earth. 

Simulation Experiments 

Experiments have been performed in which terrestrial micro-organisms have 
been introduced into simulated Martian environments, with atmospheres com- 
posed of nitrogen and carbon dioxide, no oxygen, very little water, a daily 
temperature variation from +20° to —60° C, and high ultraviolet fluxes. 




w 



50 40 'jO 60 7V 60 ~o [,u 



SO 50 40 50 60 70 «U ?0 6C ^0 -10 JO !0 40 f.0 60 '0 



70 60 50 40 W 



Figure 2. — International Astronomical Union map of Mars. In the astronomical convention, 
south is toward the top. The extent of the polar ice caps in summer can be seen at the 
top and bottom of the picture. The area Syrtis Major, at +10° latitude, 290° longitude, 
is a site of strong seasonal darkness and polarization changes, and is a suspected site of 
hydrocarbons and aldehydes. The dark area, Solis Lacus, at — 30° latitude, 90° longitude, 
is a site of strong secular changes which occur erratically and cover areas up to 1000 kilometers 
in extent. These two sites are among those of greatest interest for early exploration of Mars. 



EVIDENCE RELEVANT TO LIFE ON MARS y 

It was found that in every sample of terrestrial soil used there were a few 
varieties of micro-organisms which easily survived on "Mars." When the 
local abundance of water was increased, terrestrial micro-organisms were able 
to grow. Indigenous Martian organisms may be even more efficient in coping 
with the apparent rigors of their environment. These findings underscore the 
necessity for sterilizing Mars entry vehicles so as not to perform accidental 
biological contamination of that planet and obscure the subsequent search for 
extraterrestrial life. 

Direct Searches for Life on Mars 

The early evidence for life on Mars — namely, reports of vivid green colora- 
tion and the so-called "canals" — are now known to be largely illusory. There 
are three major areas of contemporary investigation: visual, polarimetric, 
and spectrographic. 

As the Martian polar ice cap recedes each spring, a wave of darkening 
propagates through the Martian dark areas, sharpening their outlines and 
increasing their contrast with the surrounding deserts (fig. 2). These changes 
occur during periods of relatively high humidity and relatively high daytime 
temperatures. A related dark collar, not due to simple dampening of the 
soil, follows the edge of the polar cap in its regression. Occasional nonseasonal 
changes in the form of the Martian dark regions have been observed and 
sometimes cover vast areas of surface. 

Observations of the polarization of sunlight reflected from the Martian dark 
areas indicate that the small particles covering the dark areas change their 
size distribution in the spring, while the particles covering the bright areas 
do not show any analogous changes. 

Finally, infrared spectroscopic observations of the Martian dark areas show 
three spectral features which, to date, seem to be interpretable only in terms 
of organic matter, the particular molecules giving rise to the absorptions being 
hydrocarbons and aldehydes. 

Taken together, these observations suggest, but do not conclusively prove, 
that the Martian dark areas are covered with small organisms composed of 
familiar types of organic matter, which change their size and darkness in 
response to the moisture and heat of the Martian spring. We have no evidence 
either for or against the existence of more advanced life forms. There is much 
more information which can be garnered from the ground, balloons. Earth 
satellites. Mars flybys, and Mars orbiters, but the critical tests for life on Mars 
can only be made from landing vehicles equipped with experimental packages 
such as those discussed on the following pages. 



CHAPTER II 



Mars Surface High-Resolution Near-Scan TV 



The first thing man generally does in a new and strange environment is to 
look around. This is exactly what scientists want eventually to do through 
one of the Voyager-class landing capsules on Mars by using photographs 
relayed from television cameras. This "eyes on Mars" experiment would 
offer genuine scientific merit for the following reasons. 

1. We want to know the topography immediately surrounding the capsule. 
There may be both geological and biological surprises in the landscape re- 
vealed by a televised survey. 

2. We would like to monitor the instrument operations. 

3. Scientists and laymen alike could participate in this experiment. All 
could see what the scenery of the red planet is like. 

TV cameras such as those used on Surveyor or Ranger (spacecraft used 
in lunar missions) might be adapted for use in the exploration of Mars. The 
Surveyor cameras use zoom lenses having a focal length range of from 25 mm 
(wide-angle) to 100 mm (narrow-angle). In the narrow-angle mode these 
cameras can produce a resolution of 0.25 milliradian per TV line. This means 
that at a distance of 4 meters the resolution is approximately 1 mm per TV 
line. These cameras are fitted with filters for color separation and polariza- 
tion studies. Figure 3 shows one of the Surveyor cameras. The vidicon 
image tube is mounted vertically and looks up into a mirror which can be 
rotated in elevation and azimuth to provide viewing in virtually all directions. 

The Ranger TV cameras, now well described in other reports, are also of the 
wide- and narrow-angle type. Although possessing a fixed focus, they can 
photograph in the range of approximately 1,120 miles to about ji mile. Lens 
apertures vary and are set so that pictures can be taken corresponding to 
average lighting conditions on Earth from noon to dusk. The vidicon tube 
for each camera works on a photoconductive principle similar to tubes in 
commercial television cameras. The light and dark areas of the image on the 

11 



12 



DETECTION OF EXTRATERRESTRIAL LIFE 



face plate are scanned by a beam of electrons which differentiate these light 
and dark areas by their electrical resistance. The scan lines are converted 
into electrical signals, highly amplified, converted to a frequency-modulated 
signal, sent to a 60-watt transmitter, and received on Earth. Direct mounting 
and use of this system on a capsule on the surface of Mars is not now possible. 
Nevertheless, the Ranger VII photographs of the Moon underscore the potential 
of the system as soon as technology permits Its application to the planets. 
A more sophisticated use of television cameras is illustrated by the micro- 
scope-television combination described in the next chapter. 



Mirror 



Mirror rotation 
drive motor 



Filter wheel 
assembly 




rrortllt 
drive assembly 



Focus potentiometer 



Iris potentiometer 



VIdicon tube 



Variable focal 
length lens 
assembly 



Shutter assembly 



VIdicon 
radiator 



ECU 



Figure 3. — Television 
survey camera. 



Electrical 
connectors 



CHAPTER III 



The Vidicon Microscopes 



The detection of life by looking for it sounds elementary; however, this 
seemingly simple technique is extremely complex and involves numerous 
technical problems. The usefulness of a visual method lies in the extensive 
background of classical terrestrial biological observation from the macrocosm 
to the microcosm. In addition, the morphological approach does not depend 
upon assumptions concerning the nature of extraterrestrial biochemistry. 
Certain structural attributes, with varied degree of elaboration and applica- 
tion, are not expressions of particular specific form, but of life itself. 

A television (vidicon) microscope for planetary exploration has been sug- 
gested by Dr. Joshua Lederberg of Stanford University. The investigation 
of this idea is being carried out in his Instrument Research Laboratory and in 
Dr. Gerald Soffen's laboratory at the Jet Propulsion Laboratory of the Cali- 
fornia Institute of Technology. These groups are assessing the problems of 
using the microscope as an instrument of life detection. 

Terrestrial atmosphere and soil contain a multitude of viable or moribund 
microscopic organisms. Bacteria, algae, fungi, protozoans, and diatoms are 
commonly found. Fragments of organisms and fossil forms are also frequently 
among the components. Special parts of organisms, such as seeds, pollen grains 
and spores, comprise an important fraction because of their capability of sur- 
viving rigorous environmental conditions. 

Recognition and identification of micro-organisms by microscopy is often 
difficult and uncertain; however, in many cases, characteristic morphology is 
highly indicative and sometimes conclusive. Specific form, size, symmetry, 
optical properties, surface features, pigmentation and intricate internal archi- 
tecture are among those typical details which have made the microscope useful. 
In addition to conventional use, the microscope may be extended to carry out 
microspectrophotometry, microhistochemistry and microfluorometry, which 

13 



14 



DETECTION OF EXTRATERRESTRIAL LIFE 



would provide chemical information concerning the object or materials in the 
field of view. 

The simplest model of a microscope for space use is called the "abbreviated 
microscope." This is a fixed-focus, impaction, phase-contrast instrument 




Aerosol 

in out 



Objective 
lens 




Figure 4. — The abbreviated microscope. An aerosol for carrying particles is injected into 
the instrument and is impacted onto the impaction plate through a nozzle implanted in the 
condenser lens. The objective lens and the lamp are fixed in relation to the plane of focus. 
The sample is collected through a gas-operated aerosol aspirator. The instrument has no 
mechanical moving parts. 



THE VIDICON MICROSCOPES 



15 



which offers a unique solution to the "deposition" of a sample for optical ex- 
amination (fig. 4). An aerosol sample is injected into the plane of focus of the 
microscope through an orifice in the condenser lens. The image is transmitted 
by vidicon. The lens system observes a 100-ju field with 0.5-ju resolution. 
The vidicon picture, when telemetered to Earth, would require a great deal of 
data transmission; it might take hours to send a single picture. When more 
power and larger antennas are available, and with special data handling tech- 
niques, this time may be reduced significantly. 

A more complex idea under development employs spectral and spatial 
scanning as a criterion for the selection of objects of interest. Specific ultra- 
violet absorption of particles is carried out by scanning microspectrophotom- 
etry. This has been developed to include the fluorometric capability of 
detecting the primary fluorescence of native compounds and fluorescence due 
to products formed by specific reactants. The scanning technique is also being 
investigated for use with biological stains. 

Other areas being explored are automatic focusing, changes in magnification, 
the use of more sensitive imaging devices, and improved sample preparation 
to remove the inorganic fraction. 



CHAPTER IV 



The Gas Chromatograph 



Gas chromatography has been proposed as an excellent method for detecting 
the gases of planetary atmospheres and for identifying organic chemical com- 
pounds which are of biological interest. 

The essential parts of the gas chromatograph are a long tube, or column, 
containing a powdered material which will adsorb, or bind, different gases with 
different degrees of strength and a detector that is placed at one end of the 
tube. During an analysis, the unknown sample, which usually consists of a 
mixture of gases, is forced through the column by an inert gas, or carrier gas, 
such as helium or argon. The gases of the sample that are more strongly 
bound to the material in the column pass through more slowly than the gases 
that are weakly bound. In this way different gases pass out of the column at 
different times and are indicated by the detector. (See figs. 5 and 6.) 

A basic gas chromatograph for detecting and measuring atmospheric gases 
or for analyzing organic compounds of biological interest is shown in figure 6. 
In the case of an atmospheric analysis, a sample of the atmospheric mixture 
is transported to the sa^nple injector. A constant flow of carrier gas from 
the carrier-gas storage tank is delivered to the column by the flow regulator 
and is permitted to flow continuously before injection of the sample. The 
sample is then put into the carrier-gas stream by the sample injector. The 
different gases in the mixture separate as they pass through the column, 
with each gas finally passing through the detector, and causing it to produce 
an electrical signal. The signal is fed into an electronics system where it is 
amplified and transmitted back to Earth. 

Under suitable conditions, the strength of the signal will indicate the amount 
of each gas (see fig. 7). The kind of gas is determined by the length of time 
it takes to pass through the column. The detectors used in gas chromatog- 
raphy usually detect changes in the physical properties of the carrier gas; 
for example, electrical or thermal conductivity. 

17 



18 



DETECTION OF EXTRATERRESTRIAL LIFE 



Pyrolysis 
oven 



Sample 
injector 



Flow 
regulator 




Programmer 
amplifier 
data handling 



Carrier 
gas tank 



Figure 5.— Gas chromatograph. 




Flow 
regulator 



Column 



Amplifier 
and data 
handling 



_ Detector 



Z=' Exhaust 



Thermostat 
_^___ —I 

Figure 6.— Block diagram of the gas chromatograph. 



Biological substances do not normally occur as vapors and therefore cannot 
be directly detected by gas chromatography. In the analysis of these com- 
pounds it is necessary to convert nongaseous materials to vapor form before 



THE GAS CHROMATOGRAPH 



19 



they can be analyzed by gas chromatography. This can be done in two ways. 
One way is to heat the sample at relatively low temperatures ; for example, 100° C 
to 150° C. With this treatment, some biological compounds can be con- 
verted to vapors which can be injected into the carrier gas and analyzed in 
the usual way. Other biochemical compounds cannot be vaporized so easily 
and must be heated to higher temperatures. When these substances are 
strongly heated their molecules break up into smaller molecules, some of 
which are gaseous. By analyzing these smaller molecules on the gas chromato- 
graph it is possible to tell what the original biological substances were. This 
type of analysis requires a great deal of research in order to learn how large 
molecules break down when they are heated at high temperatures. The 
oven in figure 6 is used to heat biochemical compounds in order to convert 
them to gases. 

Through the use of gas chromatographs that are designed to perform an 
analysis automatically on space probes landed on the surface of Mars it will 




Minutes ■ 



Figure 7. — Typical gas chromatogram. Zero is the time of injection. The time on the 
minutes scale, for each peak, is its retention time, and identifies the gas passing through the 
detector. The area under each peak is proportional to the amount of gas. 



20 DETECTION OF EXTRATERRESTRIAL LIFE 

be possible to determine what gases in the Martian atmosphere may be im- 
portant to Hving organisms. For example, tests for water vapor, oxygen, 
carbon dioxide, and nitrogen can be made as well as for many other gases, 
and samples of Martian soil can be collected and heated. If these samples 
contain organic matter, it will be possible to tell whether substances which 
are known to be part of living organisms are present. If proteins, nucleic 
acids, sugars or fatty substances are found, this would be strong evidence 
that life is present, although it would not be conclusive. The information 
obtained through gas chromatography, combined with information obtained 
through other experiments, would not only establish the presence of life, 
but it would tell whether or not this life was chemically the same as terrestrial 
life. 

One of the outstanding advantages of the gas chromatograph is its versa- 
tility. It can be made very complex or relatively simple depending upon 
the kind of analysis desired and the constraints of the space probe mission. 
By using a system having several columns and detectors, an instrument can 
be designed which will analyze a wide variety of biochemical substances. 
This would be desirable if there is no prior clue to the possible kinds of organic 
chemicals in an unknown mixture, such as might be the case for a sample of 
Martian soil. 

A second important advantage is that the analysis results in the separation 
of complex chemical mixtures. This feature permits confirming the analysis 
of each constituent by other methods; for example, mass spectroscopy. 

Finally, the instrumentation is readily adaptable to miniaturization and 
ruggedness of construction, which is an essential feature for instruments 
intended to perform remote automatic analysis on unmanned space probes. 

Several model instruments have been studied for application to the biological 
exploration of the solar system. These instruments range from 5 to 14 pounds 
in weight and are of various degrees of complexity. Gas chromatographs 
which can analyze planetary atmospheres in 10 seconds are being studied, as 
well as instruments which can detect tens or hundreds of gaseous compounds 
in a single analysis. Because of this extreme versatility, the scientists working 
with gas chromatography believe that it is one of the most useful methods for 
the detection of biologically relevant chemical compounds and the constituents 
of planetary atmospheres. 



CHAPTER V 

The Mass Spectrometer 



Although mass spectrometry, Hke gas chromatography, cannot prove the 
existence of life, it is an experimental tool which would enable us to learn much 
about the organic chemistry of Mars. 

The mass spectrometer approach to exobiological studies is being carried out 
under the supervision of Dr. Klaus Biemann at the Massachusetts Institute of 
Technology. Dr. Biemann has concentrated much of his experimental work 
on amino acids and peptides. This method accomplishes identification through 
the mass spectra (i.e., the distribution of the masses) of the pyrolysis products 
of the introduced samples. In one type of instrument an amino acid is heated 
near the ion source. The molecular fragments so produced vaporize off the 
sample and are accelerated according to their masses onto an electron multi- 
plier. The identification of the original amino acid is based on the charac- 
terestic masses of these fragments. 

The mass spectrometer is perhaps unique for the specific identification of 
small amounts of compounds which have been roughly classified by other 
methods. While not as sensitive as color reactions, ultraviolet absorption 
and fluorometry, mass spectrometry is an extremely versatile and powerful 
method for identifying organic compounds. The ability to recognize organic 
structures, regardless of whether they do or do not show any resemblance to 
the molecules with which we are familiar in terrestrial biology, could be 
crucially important for Martian exploration. 

The sample size for mass spectroscopy ranges from a few tenths to a few 
millionths of a milligram. Spectral interpretation is simplified if this small 
sample is not too complex. Therefore, some sample preparation is required, 
with gas chromatography being the favored method for accomplishing this. 

Mass spectrometry could also provide data on the composition of the 
atmosphere and the abundance of ratios of stable isotopes of the elements of 
low atomic number. Both of these areas are of obvious relevance to the 
biological exploration of celestial bodies within the solar system. 

21 



22 



DETECTION OF EXTRATERRESTRIAL LIFE 



C,H,CH„^CH^COOH 

5 Ci I i 

Phenylalanine 
(mass 165) 



® CH-COOH 



(mass 74) 



C^HrCH« ® 



C,HrCH«CH 

DP i. { 




HO-C,H,CHJCH^COOH ■ 
4 i.i I I 



NH, 



Tyrosine 
(mass 181) 



® CH-COOH 
/ 

NH^ 



mass 74) 




-C^H^CH^ 




Figure 8. — Origin and appearance of the mass spectra of two amino acids. 

Figure 8 shows the mass spectra of two amino acids, phenylalanine and 
tyrosine. Upon electron bombardment, certain bonds in the molecules of 
phenylalanine (top) and tyrosine (bottom) are broken to form various posi- 
tively-charged fragments which the mass spectrometer separates and records 
according to mass (see curves). Both give mass 74, characteristic of many 
amino acids, but the rest of the peaks differ because tyrosine contains one more 
oxygen atom than phenylalanine. 

Any mass spectrometer built for use in space would, of course, incorporate 
a collection apparatus for sampling, sensors to note the results, and telemetry 
equipment to communicate these results back to Earth. Such information 
would be obtained quickly with this instrument. The entire mass spectrum 
of a biological molecule can be scanned in a few seconds. The instrument 
should be designed for the determination of spectra up to a molecular weight 
of 250. 



CHAPTER VI 



The Ultraviolet Spectrophotometer 



The use of ultraviolet spectrophotometry for detecting peptide bonds is 
being studied to determine whether it can be applied to the search for life on 
other planets. This program is under the direction of Dr. Sol Nelson at 
Melpar. Since all proteins contain peptide bonds, and since all living things 
on Earth contain proteins, the detection of extraterrestrial peptide bonds 
might be consistent with the presence of living things. 

Before going any further, it would be worthwhile to explain what ultraviolet 
spectrophotometry is, and what proteins and peptides are. 

Suppose a child is in a swing that is moving at a rate of two swings each 
second. We can say that the frequency is 2 cycles per second. If you stand 
behind him and push the swing at the same frequency (2 times per second), 
the swing absorbs the energy and its amplitude increases. Your pushing 
frequency is said to be in resonance with the swinging frequency. If you 
try to push at a frequency of 3 cycles per second, it is obvious that the swing 
will not absorb the energy as efficiently. 

As another example, let us consider the case of sound. Picture a room with 
two pianos, one with a full set of strings and one with only one string — middle C. 
Now, if the keys of the complete piano are struck one at a time, you will note 
that the single string on the incomplete piano emits a sound only when middle C 
(or a note of which it is an overtone) is struck on the complete piano. Here, 
too, the single string absorbs energy and begins to vibrate when it is in resonance 
with the energy. Thus, striking a D does not cause the C string to vibrate 
because their vibration frequency is different. 

Although the examples deal with mechanical energy, the same phenomenon 
occurs with electromagnetic energy which includes X-rays, ultraviolet, visible 
light, infrared, radar and radio waves. Each of these terms applies to a range 
of electromagnetic energy. The highest frequencies are in the X-rays, and the 
lowest frequencies are in the radio. Now, if we recall that matter consists of 

23 



24 



DETECTION OF EXTRATERRESTRIAL LIFE 



molecules, and that the molecules, their atoms and their electrons are always 
vibrating, then we can expect to find some of these vibrations to be in resonance 
with the vibrations of a portion of the electromagnetic spectrum. 

If we want to study the absorption of ultraviolet light by substances, we need 
an ultraviolet spectrophotometer. This is an instrument that can separate 
ultraviolet light into bands of very narrow frequency ranges, and can measure 
the amount of ultraviolet passing through a substance. Thus, if we isolate a 

100 



90 



70 



60 



S 50 



40 



30 



20 



10 



^^ 


\ 






-rx^ 




s 

^ 


\ 










^ 


( 












r 


~y~~r 0. 057. 






-' 






jj^ 0.15% 












j 1^ 0. 3% 










] 












V 












1 












\J 











175 190 200 



275 



225 250 

Figure 9. — Absorption spectra at pH 1; Alanylglycylglycine (tripeptide). 



300 



THE ULTRAVIOLET SPECTROPHOTOMETER 



25 




A.(m>/) 
Figure 10. — Absorption spectra of soil extract (NaOH). 

band of light and pass it through a substance and find that 100 percent of the 
light has passed through, we say that the ultraviolet was not absorbed. This 
means that the substance does not have vibrations of the same frequency as the 
ultraviolet. Now, if we pass a band of ultraviolet of another frequency and we 
find that only 10 percent of the light passes through the substance, then we 
know that the light was absorbed and that the substance had a vibration of the 
same frequency as that particular band of ultraviolet. 

Proteins are large, complex molecules consisting of amino acids linked to- 
gether in long chains that are folded into characteristic shapes. The amino 
acids are held together by peptide bonds, and their combination joined in such a 
fashion is called a peptide. A combination of two amino acid molecules is a 
dipeptide; three are a tripeptide; many are a polypeptide. A protein is a large 
polypeptide, or a combination of several polypeptides. When a protein is 
hydrolyzed, it is split into peptides, and these are then split into amino acids. 
(This is what happens in the stomach and intestine when proteins are digested.) 



26 DETECTION OF EXTRATERRESTRIAL LIFE 

Now, if we study the absorption of electromagnetic energy by proteins, it 
is seen that a portion of the spectrum in the far ultraviolet region (around 
1950 A) is characteristically absorbed by the protein. Further study shows 
that the particular vibration in resonance with the ultraviolet is somewhere in 
the peptide bond. A tripeptide absorbs twice as much as a dipeptide. A 
polypeptide with 100 bonds (101 amino acids) absorbs one hundred times as 
much energy as a dipeptide. As a protein is hydrolyzed we see that the absorp- 
tion of ultraviolet light decreases, and when it is completely hydrolyzed and 
all the peptide bonds are broken, there is no more absorption of this region of 
the ultraviolet. 

Unfortunately, peptides are not the only substances that absorb in this 
region, and some confusion might result. A study of the absorption by other 
substances shows, so far, that hydrolysis does not affect it. Thus, it can be 
said for the present that if the substance absorbs far ultraviolet before and 
after hydrolysis, it is not a peptide, but if hydrolysis reduces the absorption, it 
may be a peptide. 

If further research warrants it, a small, rugged spectrophotometer will be 
built. The instrument will be able to collect a sample of Martian soil, treat 
it with solvents and place a portion in each of two quartz vessels. One sample 
will be hydrolyzed and the other will not. Then the instrument will take 
spectrophotometric readings of both samples. If the readings are different, a 
message will be sent to scientists on Earth that peptides exist on Mars. 

The ultraviolet absorption spectra of three different concentrations of 
alanylglycylglycine at pH 1 are shown in figure 9. Figure 10 illustrates the 
ultraviolet absorption spectra for sodium hydroxide extracts of soil (ratios 
are amounts of NaOH to H2O in extracting solutions). 



CHAPTER VII 

The J-Band Life Detector 



This experiment is being studied for NASA by Dr. R. E. Kay and Dr. E. R. 
Walwick at the Philco Research Laboratories and is designed for use on Mars. 

Because of the probable evolutionary history of the Martian environment, it 
is believed that Martian life will be based on similar chemical constituents and 
evolutionary principles as life on Earth. On Earth, life resides only in systems 
which are composed of molecular aggregates (macromolecules) known as pro- 
teins, nucleic acids and polysaccharides. Therefore, it is reasonable to assume 
that the detection on Mars of macromolecules having properties similar to 
proteins, nucleic acids or carbohydrates, will provide some support for the view 
that life exists on the planet. When certain dyes interact with macromole- 
cules, color changes (metachromasia) occur which can serve to identify and 
detect biological materials. The present experiments have been concerned 
with the changes produced in the absorption spectrum of a dibenzothiacar- 
bocyanine dye when it interacts with trace amounts of biological macromole- 
cules. The spectral changes occurring when this dye reacts with biological 
macromolecules are unique in regard to the diversity of the changes that occur 
and the large amount of information which can be deduced. 

In this case, the interaction of the dye with biological macromolecules always 
produces an increase in absorbance at new maxima. There are seven different 
regions of the spectrum in which absorption maximum are found. These are 
located at approximately 450, 480, 508, 535, 560, 575, and 650 m/x. The peak 
in the 650-mju region is referred to as a J-band, being named after E. E. Jelly 
who described it in detail. This absorption band is particularly interesting 
because, of the macromolecules which have been tested, only those of biological 
origin interact with the dye to produce this absorption band. This is indeed 
fortunate, since the J-band has properties which make it especially useful in 
a detection scheme. It lies almost entirely outside the absorption region of 
the normal dye absorption spectrum, and the absorption coefficient is extremely 
high. Because of this, an increase in absorbance in the J-band region occurs 

27 



28 



DETECTION OF EXTRATERRESTRIAL LIFE 



in the presence of very low macromolecule concentrations and variations in the 
reference (dye band) are negHgible. Thus, the experiment has been referred 
to as the "J-band life-detector." This title is convenient because of its brevity, 
but it focuses attention on only one aspect of the method. The program is 
concerned not only with the J-band, but also with other alternations of the 
dye spectrum which result from the interaction of the dye with macromolecules. 

The maxima which appear, and their exact wavelength, are functions of the 
macromolecule structure and the nature of its functional groups. Thus, for 
example, interaction of the dye with native deoxyribonucleic acid (DNA) 
produces a single peak at 575 mn, whereas its interaction with denatured 
DNA causes a single peak at 540 nifx. On the other hand, proteins may 
produce multiple bands which occur in the 650-, 575- and iSO-mn regions of 
the spectrum. With proteins, a band can always be produced in the 650-ot/x 
region of the spectrum; the exact wavelength of this band appears to be a 
function of the nature of the protein. Variables, such as change in acidity or 
alkalinity (pH) and temperature, cause changes in the absorption spectra of 
macromolecule-dye complexes which are related to the nature of the macro- 
molecule. In general, the method is sensitive to 0.1 to 1 microgram of 
macromolecule per ml, and the absorbance of the associated complex is 
proportional to the concentration of the macromolecule. 

The positions of the new absorption maxima appear to be a direct property 
of the spacing of the functional groups on the macromolecule, the rigidity 
of the macromolecule structure and the sequence of the anionic and cationic 
sites. The effects produced by changes in temperature and pH are apparently 
associated with modification in the folding and coiling of the macromolecule, 
the dye-macromolecule equilibrium and the ionizability of the functional 
side groups. Thus, by observing the spectral changes which occur when this 
dye interacts with a macromolecule and by appropriate manipulations of 
environmental variables, it is possible to detect trace amounts of macro- 
molecules, distinguish between macromolecules which are difficult to dif- 
ferentiate by conventional methods and obtain information about the structure 
of macromolecules and estimate the macromolecule concentration. 

It is expected that on Mars the experiment will be carried out in the 
following manner: The test capsule will acquire a soil sample, extract the macro- 
molecules and mix them with the dye solution (sample solution and prepara- 
tion). The absorbance of the dye-macromolecule mixture will then be deter- 
mined. 

In laboratory tests, a number of soil samples have been analyzed for macro- 
molecules by the scheme indicated for the Mars experiment. In each case. 



THE J-BAND LIFE DETECTOR 



29 



changes in the absorption spectrum of the dye, indicative of the presence of 
macromolecules, were observed. This was true for soils which had a total organic 
carbon content as low as 0.2 percent. Concentrated extracts from some of 
the soils, which exhibited new absorption peaks in the 535- and 650-m^ regions 
of the spectrum, were analyzed for macromolecules by conventional laboratory 
methods. Macromolecules were isolated and amino acids and monosaccha- 
rides were obtained when the macromolecules were hydrolyzed, indicating 
that the macromolecules present in the soils were proteins and polysaccharides. 
This is in agreement with the results obtained by the dye test and strongly 
indicates that the method will be very useful for the detection of macromolec- 
ular species which are characteristic of all living material as we know it. 

Figure 11 shows three absorption maxima. The first, at 505 mix, is the region 
of normal dye absorption. The others, at 575 m.n and 648 nin, are absorption 
bands due to the interaction of the dye with a 0.002-percent solution of 
oxidized ribonuclease. 




Figure 11. — Three absorption 
maxima in the J-band region. 



400 450 500 550 600 
Wavelength (millimicrons) 



CHAPTER VIII 



Optical Rotation 



To determine the presence of life on other planets through remotely con- 
trolled instruments, two factors must be considered. First, we postulate 
that life on other planets has a chemistry similar to ours. This is an obvious 
first guess and may well prove to be approximately correct. As was shown 
in the introduction, there is reason to believe that the chemical events occurring 
on the primitive Earth also occurred on other planets of the solar system. 
Secondly, what is life and how do you know when you have found it? 

"This," says Dr. Ira Blei, "brings us to the heart of the problem of the 
search for life on other planets." Dr. Blei, of Melpar, is the scientist in charge 
of the optical rotatory experiment for NASA. 

How can one design single experiments which will provide enough informa- 
tion to permit a decision to be made concerning the existence of biologically 
significant molecules.'' Life has become very difficult to define in just a few 
words. The highest form of life on Earth, man, is a collection of very complex 
molecules having certain life-like properties associated with them. At the 
other end of the scale are the many types of simple chemical substances — 
sugars for example — which are obviously not alive. Further, somewhere 
between the two extremes are systems which are sometimes "alive" and 
sometimes not: the viruses. 

So, we may look for a substance or property which is common to all life. 
One measurable property which has consistently been found in all living systems 
is optical rotation. A substance is said to possess optical activity when a 
"flat ribbon," or plane wave, of light (polarized) passing through this substance 
is twisted, or rotated, so that the flat ribbon of light emerges in a new plane. 

This ability to rotate the plane of polarized light is associated with molecular 
structure in a unique manner, just as the absorption spectroscopic characteris- 
tics are unique. Not all materials are capable of rotating the plane of polarized 



31 



32 



DETECTION OF EXTRATERRESTRIAL LIFE 



light; however, nucleic acids, proteins, and carbohydrates, all associated with 
life, do. 

To measure the ability of a substance to rotate plane polarized light, it is 
necessary to place the substance between two polarizing filters. Plane po- 
larized light passes through the substance into the second filter, which has 
been rotated so that no light can penetrate. Now, if the natural material 
can cause the plane ray to twist, some light will begin to leak through the 
second, or analyzer, filter. To restore the initial condition of the incident 
light leak, the analyzer must be rotated through a certain angle. The extent 
to which the analyzer is rotated is the measure of net optical rotation. Figure 



IP 28 Photomultiplier 




Source 



Front surface mirror 



Neutral 
filter 



Collimator lens 
Figure 12. — Optical system for optical-rotatory device. 



OPTICAL ROTATION 33 

12 shows the general layout of the optical component of the optical rotation 
device. 

An important feature of optical rotation is that it is thousands of times more 
sensitive near a spectroscopic absorption band of the substance than at wave- 
lengths removed from it. Such biological molecules as nucleic acids and 
aromatic amino acids maximally absorb in the 2600 A and 2800 A regions, 
respectively. Organic compounds formed by chemical synthesis generally con- 
sist of mixtures which rotate light in opposite directions and thus neutralize 
each other. It is a characteristic property of living things to select and 
synthesize forms which rotate polarized light in one direction. 



CHAPTER IX 



The Radioisotope Biochemical Probe: Gulliver 



This instrument, named after Swift's famous fictional traveller to strange 
places, is designed to search for microbial life on Mars. The project scientists 
for NASA are Dr. Gilbert V. Levin of Hazleton Laboratories, Inc., and Dr. 
Norman H. Horowitz of the California Institute of Technology. 

Gulliver consists of a culture chamber that inoculates itself with a sample of 
soil. The chamber contains a broth whose organic nutrients are labeled with 
radioactive carbon. When micro-organisms are put into the broth they 
metabolize the organic compounds, releasing radioactive carbon dioxide. The 
radioactive carbon dioxide is trapped on a chemically coated film at the 
window of a Geiger counter. The counter detects and measures the radio- 
activity; this information will be conveyed to a radio transmitter which will 
signal it to Earth. Gulliver can detect growth, as well as metabolism, by 
virtue of the fact that the rate of carbon dioxide production increases ex- 
ponentially (geometrically) in growing cultures. Exponential production of 
carbon dioxide would provide strong evidence for life on Mars and would 
make it possible to estimate the generation time; that is, the time required for 
doubling the number of organisms in the culture. 

In addition to a culture chamber and counter (actually a group of counters 
in anticoincidence circuitry), Gulliver contains a built-in sample collector. 
This mechanism consists of two 25-foot lengths of kite line and chenille wound 
on small projectiles. The windings are made in the manner of harpoon lines 
to prevent snagging, and the strings are coated with silicone grease to make 
them sticky. When the space package arrives on Mars, a miniaturized pro- 
grammer will take charge of Gulliver (actually, at least two Gullivers will be 
used, one as a test instrument and the other as a control). The projectiles 
will be fired, deploying the lines over the surface of the planet. A tiny motor 
inside the chamber will then reel in the lines, together with adhering soil 
particles. After line retrieval, the chamber of Gulliver will be sealed, and an 

35 



36 



DETECTION OF EXTRATERRESTRIAL LIFE 



ampule inside will be broken, releasing the previously sterilized radioactive 
medium onto the lines. 

Both the test and control Gullivers will be inoculated with soil simulta- 
neously, as described above, but the control instrument will be injected with 
a metabolic poison soon after inoculation. The purpose of this step is to 
make sure that any carbon dioxide evolution that is detected is of biological 
origin. If space is available for more than two Gullivers, the nature of the 
antimetabolite can be varied so as to provide information on the chemical 
sensitivity — and therefore on the chemical nature — of Martian life. 

In principle, Gulliver is capable of performing many different kinds of 
metabolic and biochemical experiments. For example, a modified version of 
the current model would be able to detect photosynthesis by measuring the 
effects of light and darkness on the evolution of carbon dioxide. This ap- 
plication of Gulliver has been demonstrated in the laboratory. It is important 




Figure 13. — A working model of Gulliver, tested under a variety of conditions. 



RADIOISOTOPE BIOCHEMICAL PROBE: GULLIVER 37 

because we can be certain that if life exists at all on Mars, there will be at 
least one photosynthetic species that captures energy from the Sun. 

The composition of the medium is one of the most interesting problems 
connected with the Gulliver experiment. Obviously, the success of the ex- 
periment depends on the correct choice of nutrients. There are reasons for 
believing that if life exists on Mars it will be carbonaceous life, as it is on Earth. 
One can therefore feel reasonably confident that organic compounds of some 
kind will be metabolized by Martian organisms. However, as the number of 
possible organic compounds is virtually limitless, this premise does not narrow 
the range of choices very much. What we need for the Gulliver medium are 
organic substances that are readily decomposed into carbon dioxide by living 
organisms and that are of widespread occurrence in the solar system. This 
problem can be approached experimentally. In fact, the experiment has 
already been done and has been referred to in the introduction to this book; 
that is, the experiment of irradiating a mixture of gases simulating the primitive 
atmosphere of the Earth and planets. As Dr. Stanley Miller first showed, this 
experiment yielded a number of organic acids, such as formic, succinic, and 
lactic acids. These acids have exactly the characteristics referred to above: 
they are readily metabolized to carbon dioxide by terrestrial life, and there is 
reason to believe that they were formed in large amounts on primitive Mars. 
It is contemplated that these and a number of other compounds of a similar 
nature will be among the radioactive nutrients in the Gulliver medium. 

Several working models of Gulliver have been built. The model shown in 
figure 13 has been tested under a variety of conditions: from the sand dunes 
of Death Valley to above tree-line at the 12,000-foot elevation on White 
Mountain, California, and from the salt desert of southern California to the 
woods of Rock Creek Park in Washington, D.C. In all of these places, 
Gulliver was able to detect microbial life in a matter of a few hours. 



CHAPTER X 



The Wolf Trap 



When Professor Wolf Vishniac conceived a device to search for life in space 
it was inevitable that his biologist friends would name it the "Wolf trap." 
The original Wolf trap was built to demonstrate on Earth the feasibility of 
detecting automatically the growth of micro-organisms on Mars. When 
operated either on the laboratory floor or outdoors, the feasibility model signals 
bacterial growth within a few hours after activation. 

The heart of the Wolf trap is a growth chamber with an acidity (pH) detector 
and a light sensor; the former senses the changes in acidity which almost in- 
evitably accompany the growth of micro-organisms, while the latter detects 
changes in the amount of light passing through the growth chamber. Micro- 
organisms, such as bacteria, turn a clear culture medium turbid (cloudy) 
when they grow. It is the change in turbidity which the light sensor measures. 
The pH measurement complements the turbidity measurement by providing 
an independent check on growth and metabolism. When either or both of 
these changes occur, the sensors can communicate this information to a tele- 
metering device which in turn relays the results back to Earth. 

The reason for first searching for micro-organisms on Mars is that even in 
the absence of higher plants and animals, the basic ecology (the interactions 
between the organisms in a biological community) would not be changed; it is 
possible to maintain a planetary ecology by micro-organisms alone, though not 
by animals and higher plants in the absence of micro-organisms. 

The biological reasoning behind the particular approach of the Wolf trap 
was presented by Professor Vishniac as follows. All of the organisms of an 
environment must have a source of raw materials and energy for growth. 
Some, like the green plants, can use light energy to manufacture energy-rich 
chemicals (food); this process is named photosynthesis. Others, like humans, 
must consume either the photosynthetic plants, or animals which subsist 

39 



40 



DETECTION OF EXTRATERRESTRIAL LIFE 



on the plants, for energy requirements. In photosynthesis plants consume 
carbon dioxide; animals eat the plants and produce carbon dioxide. Such 
an interdependent cycling of raw materials is common within a biological 
environment. A consideration of a known environment allows one to predict 
with reasonable accuracy the type of micro-organism that will flourish in it. 
Such predictions have nothing to do with the size and shape of the micro- 
organism, nor with its microscopic appearance or its molecular structure. 
They only deal with its physiology: activities, such as photosynthesis, which 
would enable an organism to flourish in such an environment. 

These predictions are the basis for the several culture media now being con- 
sidered for inclusion in a Mars-bound Wolf trap. The most important con- 
sideration in preparing these media is the knowledge that Mars lacks oxygen 
in its atmosphere. Hence, a number of media are being devised to support 
the life of probable anaerobic micro-organisms. A variety of media allows 
the biologist to test fundamental assumptions about the nature of life and its 
chemistry, and increases the likelihood of detecting at least one possible 
life form. 

The detection principle of the Wolf trap is susceptible to a variety of modifica- 
tions. The first device can be a simple unit to meet the weight and power 
requirements of early spacecraft, or it can be an elaborate multichambered 
experiment with varied media as mentioned above. The latter, of course, 
would have the greater scientific value. 

The feasibility model has been completely redesigned, and a new model — 
the "breadboard" model — has been built incorporating changes to make it 
suitable for space flight (fig. 14). One improvement is a more sensitive method 
of detecting turbidity. The intensity of a beam of light passing through a 
turbid bacterial suspension will be reduced since some of the light is scattered 
to the sides. Instruments which can measure this reduction in direct light 
intensity "see" turbidity when 100 million organisms per milliliter are present. 
The unaided eye is a better detector since it can tell if a suspension is cloudy 
at a concentration of roughly 5 million organisms per milliliter. At least a 
thousand-fold greater sensitivity is possible by measuring the light scattered 
to the sides by the suspended organisms, rather than measuring the reduced 
intensity directly. The particular optical geometry which has been selected 
for the Wolf trap measures light scattered at an angle of approximately 20° 
off the forward beam. This system is shown in figure 15. 

The response of the first model was a simple yes-no answer. It is more 
informative to continously measure the change in turbidity as a result of 
microbial growth and telemeter to Earth the magnitude of the change. From 



THE WOLF TRAP 



41 



this is would be possible to plot a growth curve. Similarly, a change of acidity 
can be signaled by the pH detector in terms of rate change, rather than just 
a yes-no signal. 

An essential feature of the Wolf trap operation is the sampling system. 
Originally a vacuum chamber was used to gather a sample of dust. When 
the Wolf trap was placed on the floor, a fragile glass shield was broken, allowing 



High pressure gas 
reservoir for sample 
collector 



Solenoid-operated 
gas valve 



Electronics 
are tioused 
in a 2x 3x 5" 
box beneath 
the gas 
supply 



Media reservoir and 
culture chamber 

Housing for growth 
chambers, optics, 
and sensors 




inches 



Pressure 
regulator 



High pressure line 
to sample collector 



pH probes 



Pickup 
arm 



Dust shroud - sample 
nozzle is within 
the shroud 



Figure 14. — Wolf trap experimental breadboard with cover removed. The Wolf trap measures 
5X7X7 inches with the cover in place. The sample-collector is extended on the right. 
The black bottle on the left is the pickup-gas reservoir. Immediately to its right is a 
release valve and a pressure regulator which are connected to the pickup by the Teflon 
tubing. The electronics are packaged underneath the gas reservoir, gas valve, and 
pressure regulator and cannot be seen in this photograph. In front of the assembly, 
just to the right of center, are the media reservoir and media dump mechanisms. The 
culture chamber and sensor unit is partially obscured beneath the media reservoir. 



42 DETECTION OF EXTRATERRESTRIAL LIFE 

the internal vacuum to suck dust into the culture chamber. The sampling 
mechanism of the breadboard model, like the early model, is based upon the 
sucking up of dust. However, instead of a "packaged" vacuum, compressed 
gas forced through a constricted throat produces a partial vacuum which 
sucks particles into the collection nozzle and carries them from there to the 
culture chamber. 

When the soil inoculum is initially introduced into the culture chamber 
of the breadboard there is a relatively high signal which drops rapidly as 
the heavy sand-sized particles settle out of the suspension. The very small 
particles settle out of the suspension more slowly. Superimposed on this 
soil settling curve is the growth curve of the organisms. Starting from some 
low population level, the microbes begin to multiply. When the number of 
organisms is large enough (around 100,000 per milliliter in the present device) 
they begin to form a significant amount of the signal. 

Naturally, the system cannot discriminate between soil and micro- 
organisms. The Wolf trap could send a signal change even if there were 
nothing living on Mars, as, indeed, could any of the other life-detection devices. 
Suppose for instance, the Wolf trap lands on Mars and almost immediately 
signals a marked change in the culture medium; the signals show dense tur- 
bidity and the acidity increases greatly. About all such data would mean 
would be that the Martian surface is extremely dusty and the dust extremely 
acidic. However, if only a few of the chambers indicate change, and the 
the changes are signaled over the course of several hours or a day, then it 
can be reasonably concluded that changes have taken place as a result of 
microbial activity, especially if the turbidity signal increases exponentially 
(doubled every hour or so), instead of climbing at a constant rate. 

Sample acquisition poses one of the most difficult engineering problems in 
the Wolf trap, as in other life-detection devices. Light scattered by an 
abundance of small colloidal-sized soil particles might saturate the detectors, 
allowing the growth of organisms to go undetected. It would be equally 
unfortunate if an insufficient sample were collected. The concern over the 
sampling problem is reflected in figure 14, where fully half the volume of 
the experimental breadboard is taken up by sampling system components. 
Although it is more complex, the Wolf trap breadboard is less than one-third 
the size and one-sixth the weight of the original feasibility model. Yet the 
device is still not as compact as possible. The design engineers of the Wolf 
trap point out that the bulky solenoid-operated valves in the breadboard can 
be replaced by one-shot rupture diaphragms in the flight model. This would 
represent a considerable saving in weight and space. 



THE WOLF TRAP 



43 



The next step is greater refinement of the entire system to reduce its size, 
increase its detector sensitivity, improve the S'ample collection efiiciency, and 
fully qualify the instrument for space flight so that the Wolf trap will be ready 
for installation in a Mars-bound spacecraft. 



Lamp feedback 
regulator 





Amplifier 



Lamp 
Collimating lens 

Growth chamber 

Focusing lens 

Occulting disk 
Photodetector 



Figure IS. — Wolf trap optics. 



CHAPTER XI 



The Multivator Life-Detection System 



The multivator is a miniature laboratory for conducting a variety of bio- 
chemical or biological experiments on Mars. The nature of the experiments 
is limited only by those biological properties which can be measured by a 
photomultiplier as an output transducer. The device was conceived by 
Dr. Joshua Lederberg at Stanford University. The experiment which has 
received Dr. Lederberg's particular attention is the detection of phosphatase 
activity. This is because: 

1. phosphatase is widespread among terrestrial organisms; 

2. it catalyzes the hydrolysis of phosphate esters with moderate specificity; 

3. it is involved with the role of phosphorus in metabolism and energy 
transfer which may be a universal characteristic of carbon-based aqueous 
living systems; and 

4. it is capable of being detected with relatively high sensitivity. 

A functional test for the presence of hydrolytic enzymes, such as phosphatase, 
detects the catalysis of AB-j-HoO tfl^i! AH + BOH. The basis of the phos- 
phatase test is the release of AH which differs from AB in being fluorescent. 
In this case, A is a fluorescent residue and B is a phosphate that permits the 
fluorometric assay of phosphatase. The multivator is designed to carry out 
such assays as well as many others. It does this by mimicking in miniature 
a great many of the kinds of instruments used in a typical biochemical labora- 
tory. The basic elements of the instruments are a light source followed by a 
filter; the sample under investigation; another filter centered at either the 
same wavelength as the excitation filter for colorimetry or light scattering, or 
at a different wavelength if fluorometric observations are to be made; and 
finally, a light detector, usually a photomultiplier. Figure 16 shows several 
cut-away views of the multivator. 

The most recent version of the multivator consists of 15 modules arranged 
in a circle around an impeller (figs. 17 and 18). Each of the modules basically 

45 



46 



DETECTION OF EXTRATERRESTRIAL LIFE 



consists of a reaction chamber, solvent storage chamber, tapered valve pin, 
explosive-charge bellows motor, and a filtered light source. The entire solvent 
chamber is sealed prior to operation by a thin diaphragm which is placed in 
front of the pointed valve tip. 

In operation, dust-bearing air is drawn through the impeller and in front 
of the reaction chambers. The impeller imparts sufficient velocity to particles 
above lOjit in diameter to fling them into the reaction chambers where they 
tend to settle. Upon completion of the particle-collecting operation, the 
explosive-charged bellows motors are electrically ignited. Expansion of the 
bellows results in the sealing of the reaction chambers and the injection of the 
solvent. The substrate materials, which have been stored dry in the reaction 
chambers during flight, are dissolved and the reaction begins. After a preset re- 

MULTIVATOR CHAMBERS 




Electronics 



P.M. tube 



Reaction chamber 
Assembly 




1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
10. 



Motor and impeller 
Ligtit source 
Valve stem and piston 
Injector-seal unit housing 
Solvent chamber 
Bellows motor 
Photomultiplier tube 
Window 

Reaction chamber 
Reaction chamber unit block 



Figure 16. — Layout of the multivator assembly. 



THE MULTIVATOR LIFE-DETECTION SYSTEM 



47 



action time, the excitation lamps are turned on sequentially and the light signal, 
or fluorescent level in the case of the phosphatase assay, is detected by the 
photomultiplier tube. This information is then reduced to digital form and 
transmitted. One reading per chamber every 15 minutes would be satisfactory, 
requiring a fraction of a bit per second for telemetry. Certain chambers of 
the instrument are designed so that they will not collect soil. This permits a 
comparison of the behavior of the solvent-substrate mixtures subjected to the 
same conditions of voyage and Martian environment with the results from 
those reaction chambers receiving dust samples. This helps to ensure that 
the information concerning a sign of life is not due to a faulty test. 

Modular design of the multivator offers several advantages. First, the 
entire multivator becomes potentially more reliable with 15 independently 
operated modules. Secondly, each module may be filled with different types of 
solvents, thereby increasing the range of experiments that can be performed 
with a single multivator package. Thirdly, the modular design allows more 
flexibility in making the final choice of the actual experiment to be performed. 
It also permits postponing this choice to a relatively short time before the 
launch date of the mission. More than a full complement of modules could 
be under design and development; postponement of final choice would not 
interfere with orderly spacecraft development and construction as long as the 
experiments met the very simple interface parameters characteristic of the 
multivator experimental modules. 




Figure 17. — Multivator, with housing partially 
removed. 



Figure 18. — Assembled 
multivator. 



CHAPTER XII 



The Mars Mariners and Voyagers 



The first spacecraft destined for Mars will be Mariner C, a NASA planetary 
flyby scheduled for launching in 1964. 

Mars and Earth both orbit the' Sun in the same direction, but not at the 
same speed or distance. The mean distance of Earth from the Sun is 93 
million miles, while the mean distance of Mars from the Sun is 141 million 
miles. Earth makes one revolution around the Sun each 365/4' days, while 
Mars revolves around the Sun once every 687 earth days. 

The maximum distance between Earth and Mars is about 247 million 
miles, which occurs at the aphelion conjunction. However, when Mars is 
at opposition, the two planets (Earth and Mars) can be as close together as 
34.5 million miles or as far away from each other as 63 million miles. Op- 
positions are usually considered in planning missions to Mars. It is emphasized 
that neither spacecraft launch nor encounter would occur exactly at these 
opposition distances because the planets are in orbital motion at different 
velocities, as was already mentioned. From a search-for-life point of view, 
it is important to launch so that arrival coincides with those times when the 
wave of darkening on Mars is most pronounced. 

Mariner C is not intended to land on Mars, but to fly past it at a distance of 
about 15,000 km. It will carry instrumentation to obtain data on inter- 
planetary dust and plasma and to take television photographs of Mars. In 
addition, experiments are to be aboard to obtain data on the magnetic field and 
cosmic rays. The final dimensions of Mariner C will be similar to Mariner II 
which flew past Venus on December 14, 1962. 

The hexagonal framework of Mariner II housed a liquid-fuel rocket motor 
for trajectory correction. It had six modules or compartments containing the 
attitude control system, electronic circuitry for the scientific experiments, 
power supply, battery and charger, data encoder, and command subsystem 
for receiving and obeying signals from Earth, digital computer and sequencer, 
and radio transmitter and receiver. 

49 



50 



DETECTION OF EXTRATERRESTRIAL LIFE 



The solar panels, with 9,800 solar cells, collected energy from the Sun and 
converted it into electrical power. Two-way communications were supplied 
by the receiver/transmitter, two transmitting antennas and the command 
antenna for receiving. Stabilization for yaw, pitch, and roll was provided by 
10 cold-gas jets mounted in four locations and fed by two titanium bottles. 

A later Mariner will carry additional devices past Mars in 1966-67. If 
an instrumented package does land on the Martian surface it will be to de- 
termine the density profile of the Martian atmosphere. Not until 1969, 
1971, or 1973 will actual life-detection devices, using systems evolved from 
Mariner-level payloads to larger payloads of the Voyager class, be considered 
for effective surface landing and operation. 

One of the flyby experiments may consist of an infrared scanning system 
capable of measuring reflected visible radiation, emitted surface radiation 
(thermal), and radiation absorbed by atmospheric water vapor. Figure 19 
shows the general optical scheme for the instrument. This type of Mars 
"mapping" will provide useful information with respect to microenvironments 
for possible extraterrestrial life. 



Filter wheel 



Water vapor absorption detector 
(lead sulfide cell) 



Secondary 
mirror 




Thermal detector (bolometer) 



Visible radiation detector 
(silicon cell) 



Figure 19. — Optical schematic diagram for Mars scanner. 



Bibliography 



Chapter I 

deVaucouleurs, G.: Physics of the Planet Mars. Faber and Faber (London), 1954. 

Sagan, C. : On the Origin and Planetary Distribution of Life. Rad. Res., 15: 174, 1961. 

Sagan, C. : Exobiology: A Critical Review. Life Sciences and Space Research II, M. Florkin, 
ed.. North Holland Publishing Company (Amsterdam), 1964. 

Sagan, C. and Kellogg, W. VV. : The Terrestrial Planets. Ann. Rev. Astronomy and Astro- 
physics, 1: 235, 1963. 

Urey, H. C: The Planets. Yale University Press, 1952. 

Whipple, F. L. : Earth, Moon and Planets. Revised edition. Harvard University Press, 
1963. 

Chapter III 

Lederberg, J.: Exobiology: Experimental Approaches to Life Beyond Earth. Science in 
Space, L. V. Berkner and H. Odishaw, eds., McGraw-Hill, 1961, pp. 418-421. 

Chapter IV 

Knox, J. H.: Gas Chromatography. John Wiley and Sons, 1962. 

Landoune, R. A. and Lipsky, S. R.: High Sensitivity Detection of Amino Acids by Gas 

Chromatography and Electron Affinity Spectrometry. Nature, 199: 141, 1963. 
Oyama, V. J.: Uses of Gas Chromatography for the Detection of Life on Mars. Nature, 

200: 1058, 1963. 

Chapter V 

Benyon, J. H.: Mass Spectrometry atid Its Application to Organic Chemistry. D. Van Nostrand 

and Company, 1960. 
Biemann, K., Seible, J. and Gapp, F.: Mass Spectrometric Identification of Amino Acids. 

Biochem. Biophys. Res. Commun., 1: 307, 1959. 
Biemann, K. and Vetter, W.: Quantitative Amino Acid Analysis by Mass Spectrometry. 

Biochem. Biophys. Res. Commun., 2: 30, 1960. 

51 



52 



DETECTION OF EXTRATERRESTRIAL LIFE 



Chapter VI 

Nelson, S.: Absorption in the Far Ultraviolet by the Peptide Bond. 
Annual Meeting of the Biophysics Society, 1964. 



Abstracts of the Eighth 



Chapter VII 

Kay, R. E., Walwick, E. W. and Gifford, C. K.: Spectral Changes in Cationic Dye Due to 
Interaction with Macromolecules. Part 1. Behavior of Dialysate in Solution and the 
Effect of Added Macromolecules. Part 2. Effects of Environment and Macromolecular 
Structure. /. Phys. Chem., 68: 1896-1906, 1907-1916. 

Chapter VIII 

Carroll, B. and Blei, I.: Measurement of Optical Activity: New Approaches. Science, 142: 

200, 1963. 
Djerassi, C. : Optical Rotatory Dispersion. McGraw-Hill, 1960. 

Chapter IX 

Levin, G. V., Heim, A. H., Thompson, M. F., Horowitz, N. H. and Beem, D. R.: Gulliver, 
An Instrument for Extraterrestrial Life Detection. Life Sciences and Space Research II, 
M. Florkin, ed., North Holland Publishing Company (Amsterdam), 1964. 

Levin, G. V., Heim, A. H., Clendenning, J. R. and Thompson, M. F.: Gulliver — 
A Quest for Life on Mars. Science, 138: 114, 1962. 

Chapter X 

Vishniac, W.: The Wolf Trap. Life Sciences and Space Research II, M. Florkin, ed.. North 
Holland Publishing Company (Amsterdam), 1964. 



Chapter XI 

Levinthal, E.: Multivator — A Biochemical Laboratory for Martian Experiments. Life 
Sciences and Space Research II, M. Florkin, ed.. North Holland Publishing Company 
(Amsterdam), 1964. 



Suggested Reading: Background and 
Introductory Information 



Calvin, M.: Communications: From Molecules to Mars. JIBS Bulletin, 12: 29, 1962. 
Darwin, C. : On the Origin of Species (a facsimile of the first edition). Harvard University 

Press, 1963. Many other editions exist. 
Horowitz, N. H.: Biology in Space. Fed. Proc, 21: 687, 1962. 
Horowitz, N .H.: The Design of Martian Biological Experiments. Life Sciences and Space 

Research II, M. Florkin, ed., North Holland Publishing Company (Amsterdam), 1964. 
Horowitz, N. H. and Miller, S. L.: Current Theories on the Origin of Life. Fortuhritte der 

Chemie organischer Naturstojfe, 20: 423, 1962. 
Lederberg, J.: Exobiology Approaches to Life Beyond Earth. Science, 132: 393, 1960. 
LwofF, A.: Biological Order. MIT Press, 1962. 
Mamikunian, G. and Briggs, M. H., eds.: Current Aspects of Exobiology. Pergamon Press, 

1965. 
Merrill, P. W.: Space Chetnistry. University of Michigan Press, 1963. 
Miller, S.: The Mechanism of Synthesis of Amino Acids by Electric Discharges. Biochemica 

and Biophysica Acta, 23: 480, 1957. 
National Academy of Science — National Research Council: A Review of Space Research. 

Publication 1079, Chapter IX, 1962. 
Quimby, F. H.: Some Criteria of Living Systems Useful in the Search for Extraterrestrial 

Life. Developments in Industrial Microbiol, 5: 224, 1964. 
Thomas, S.: Men of Space — Profiles of Scientists Who Probe for Life in Space. Vol. 6, Chilton 

Publishing Company, 1963. 
Vishniac, W.: Terrestrial Models for Extraterrestrial Organisms. Life Sciences and Space 

Research II, M. Florkin, ed., North Holland Publishing Company (Amsterdam), 1964. 
Weisz, P. B.: The Science of Biology. McGraw-Hill, 1949. 

Young, R. S. and Ponnamperuma, C. ; Early Evolution of Life. Biological Sciences Cur- 
riculum Study No. 11, W. Auffenberg, ed., D.C. Heath and Company, Boston, 1964. 



53 

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