Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 428


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 427
CHAPTER 21 THE USE OF MARTIAN MATERIALS IN THE SEARCH FOR MARTIAN LIFE ALEXANDER RICH The exploration of Mars will involve both a search for possible life as well as a chemical characterization of the planet. It is possible that these two activities can be carried out jointly in that the procedures developed for chemical characterization can also be usefully employed in the detection of living systems. One of the problems we encounter in the search for extraterrestrial life is the question of its similarity to life as we know it on this planet. Condi- tions on Mars are such that they probably could support terrestrial life. Accordingly, experiments have been designed to be used in conjunction with a soft landing on Mars in which samples of potentially life-containing Martian matter are inoculated into reaction vessels filled with nutrients which would support growth of a wide variety of terrestrial organisms. The rationale of these experiments is that the detection of growth would cer- tainly lead us to the conclusion that life does exist on Mars. These experi- ments should be carried out but we should also consider a different class of experiments in which we make no presuppositions about the nature of Martian life. In these experiments, we do not try to speculate about the type of metabolism or the nature of Martian materials which have been utilized by Martian life, but instead we utilize the materials available on the planet directly in an attempt to detect life. An example of the danger of presupposing something about the Martian 427

OCR for page 427
428 MARTIAN LANDINGS: UNMANNED environment is the natural tendency which we have to think of life and its chemical reactions in an aqueous medium. The possible hazard of this is illustrated by some recent work from Pimentel's laboratory. They have found that it is possible to match the reported infrared bands in the Martian atmosphere with a 1:1 mixture of D2O and HDO. It was suggested that there is a large amount of deuterium relative to hydrogen in the Martian environment, and much greater than that which prevails in the terrestrial environment. While it eventually developed that the disputed infrared spectrum was of terrestrial and not of Martian origin, it raised the possi- bility that Martian life might exist in an environment with a different isotopic composition from that found on Earth. If this is indeed the case, then the use of terrestrial H2O would poison these organisms. It has been shown in experiments carried out by J. J. Katz that simple organisms are unable to adapt to very drastic changes from H2O to D2O or vice versa even though these organisms can be induced to grow on pure D2O if the transition is made very gradually. In the experiments proposed here, we would not supply terrestrial water. Instead we would collect an appropriate solvent from the Martian environment, concentrate it by one of the tech- niques described below and then attempt to detect Martian life directly in a medium supplied from Martian material. LIFE DETECTION METHODS Any experiment designed for the detection of life is carried out by per- turbing the system in some manner and then making measurements to detect metabolism or multiplication. The perturbation in the experiment discussed above consists in inoculating Martian matter into a reaction vessel rilled with terrestrial nutrients. Following this, turbidity is measured, or the incorporation of radioactive material is detected associated with meta- bolic activity. Since we must acknowledge the possibility of destroying Martian life by using terrestrial materials (and terrestrial assumptions about life) we should ask what is the minimum perturbation that we can apply to a life detecting system that is consonant with the actual detection of life. The simplest experiment of this type would be one in which a portion of Martian matter is heated slightly and then a thermal analysis carried out to detect subsequent metabolic activities by Martian microorganisms which are now subjected to a higher ambient temperature. Experiments of this type have been described elsewhere in this document. Another type of minimum perturbation experiment is one in which a sample of Martian matter is sterilized, for example, by raising it to a very high temperature adequate to kill terrestrial organisms and therefore pre-

OCR for page 427
Use of Martian Materials in Search for Martian Life 429 sumably also Martian microorganisms. This cooled Martian material could then be reinoculated with unheated, unsterilized Martian matter and the sample observed for signs of increased metabolic activity. This might occur because of the presence of more metabolic nutrients in the sterilized sample of Martian material which could be utilized by the organisms of the inoculum. A common problem in all of these analyses is the type of perturbation that we must introduce into the system in order to carry out the detection of metabolic activity. The simplest type of detection might be that obtained by thermal analysis as mentioned above. Another method for detecting metabolic activity might involve neutron activation of "sterilized" Martian material which is then exposed to Martian organisms. Detection in this case may involve looking for the end products of metabolic activity. Alternatively, another type of detection system might involve the utilization of C14 O2, C14-glucose or P32-phosphate or other radioactive materials that are of terrestrial origin, supplied by the lander. This tracer material may then participate in the metabolism of Martian organisms even though the bulk of the nutrients themselves are not supplied by the lander but rather are obtained from Martian material itself as described below. THE CHEMICAL PROCESSING OF MARTIAN MATERIAL TO COLLECT NUTRIENTS An important type of experiment is one that would involve the isolation and concentration of chemicals from the Martian terrain that could then be fed to samples of Martian matter that we suspect are contaminated with Martian microorganisms. In short, Martian matter would be subjected to chemical purification processes in the hope of concentrating nutrients that would then enable Martian microorganisms to proliferate in such a way that a positive answer could be obtained in a life detection experiment. In the execution of this project we may imagine that we have developed, for example, ten small chemical extractions modules that serve to process and concentrate Martian matter in various ways. For example, one might simply filter the materials and accumulate smaller particles, and exclude larger particles. Such a simple screening by size would select finer particles which have larger surface areas and this may represent a type of primitive chemical fractionation. Another method might use a flotation technique in a non-aqueous solvent followed by the isolation of the lighter materials. This might lead to the accumulation of oil-like Martian constituents. Another process might involve solubility in water or other solvents, fol- lowed by an extraction of the material from the solvent with subsequent

OCR for page 427
430 MARTIAN LANDINGS: UNMANNED drying. This would be a simple chemical extraction procedure. Another technique might involve volatilization and then condensation to collect the more volatile Martian components. Various techniques for chemical puri- fication might then also be associated with a subsequent chromatographic isolation that might then produce materials beginning to approach chemical purity. The chemical techniques that can be employed are numerous. For example, another process might involve the acid hydrolysis of Martian matter followed by the concentration of a hydrolysate. This would tend to convert polymeric material into monomers that might be readily utilized by microorganisms. The net result of all of these chemical fractionation and extraction procedures would be the accumulation of semi-purified Martian materials. These could be used in a double manner, on the one hand to test their value as potential nutrients for Martian organisms and, alternatively, the chemical analysis of these components would be a useful step in beginning the chemical characterization of the Martian environment. With these ten different types of chemical concentrates as described above, it would then be possible to add these materials into samples of Martian matter suspected of containing microorganisms and then to assay for the signs of metabolic activity. It would, of course, be possible to pro- gram a system to use mixtures of various products of the purification proc- ess to see whether they may be more effective than some of the components extracted singly. Finally it would be possible to construct, very simply, a program that would optimize the effect of adding these various constituents. Analysis of these materials thus gives us some primitive information con- cerning Martian biochemistry. One could think of a fairly simple auto- mated laboratory that could carry out this kind of experiment and would, in effect, carry out logical checks to determine whether positive results were consistent. Another significant consequence of this type of system is that chemical analysis could be carried out on each of the products isolated by these various techniques. In some cases, the material could be analyzed by infra- red spectroscopy, gas chromatography or mass spectrometry. This infor- mation would be of direct importance itself, independent of its effect on the biological experimentation since it would contribute to a knowledge of the chemical state of the planet. A positive result in the biological experi- ment would, however, give us direct information about some parameters of Martian life and allow a comparison with what we observe in terrestrial life. In summary, it may be possible to detect life on Mars through the use of chemical nutrients extracted on the planet by the landing apparatus. This type of experiment allows us to minimize our assumptions regarding the nature of Martian life and, at the same time to obtain some direct information regarding the chemical composition of the planet.

OCR for page 427
PART VIII MARTIAN LANDINGS: MANNED

OCR for page 427