Page:Concepts for detection of extraterrestrial life.djvu/30

20 be possible to determine what gases in the Martian atmosphere may be important to living 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 versatility. 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.