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A mass spectrometer is used to analyze the gas phase in a number of reaction vessels filled with Martian soil. By choosing appropriate incubation conditions this instrument can be used to perform a wide spectrum of experiments ranging from the observation of general indices of life, i.e. processes and patterns unexplainable by physico-chemical mechanisms, to assays utilizing isotopes which probe for specific metabolic processes. Of particular interest is the in situ incubation in which a Martian soil sample is maintained at a constant temperature and its gas phase composition analyzed with time. Properly interpreted, this is a very general life-detection probe which makes minimal assumption as to the nature of Martian biology. Other assays and measurements concerning the soil and the atmosphere compatible with this method are also described.

The studies dealing with the detection of life on planets and in space will have two periods. The first period will be associated with the application of automatical devices, which will detect living creatures, whereas the second, more late, period will be concerned with the investigations provided by man himself. In these studies one should proceed from the idea of life on the Earth, and, consequently, look for living creatures containing no water, no carbon dioxide, etc. only after obtaining negative results in searching for creatures similar to those living on the Earth. The whole course of "chemical evolution" on the Earth proves the necessity of the detection on other planets of heterotrophic microorganisms at first, and only afterwards to look for specialized forms, i.e. chemo- and photoautotrophs. It is usually underestimated that as a result of adaptation to certain ecological conditions existing on planets living creatures may appear, which will distinctly differ in their biological properties from terrestrial forms. At present there is no faultless investigation which is able to prove to existence of cosmobionts in meteorites. The appropriate experiments convince us that soil bacteria. may penetrate into the central parts of meteorites, which have been lying in the ground. Samplings at high altitudes with the aid of aerostats or the rockets are difficult to provide because of the possibility of pollution of samples by terrestrial microbes. It is therefore necessary to elaborate special devices and new methods for sampling. The most perfect instrument for the detection of microorganisms will be a device, which will record the multiplication rate of microbes in the liquid media simultaneously by means of different methods: manometry, nephelometry, potentiometry and the determination of radioactive carbon dioxide which is extracted during the breakdown of organic substances.

Among the most important factors limiting the active life of animal organisms in Martian conditions are low atmospheric pressure and insignificant amounts of oxygen in the atmosphere (no more than 0.15% of the Earth's atmosphere). The experiments with aerobic protozoon C. maupasi have shown that in conditions of hermetically sealed chambers, for instance in 2.5 liter anaerostats, the protozoon can survive for a long time and reproduce in an atmosphere of air or nitrogen containing 1 or 0.0005% oxygen at a pressure from 15 mm Hg and higher. At the atmospheric pressure 10 mm Hg we observed a considerable decrease in the survival percentage and no reproduction. The exposure to 5 mm Hg resulted in a 100 per cent mortality of the protozoon. In a specially-constructed chamber "Photostat", in which current atmosphere pressure were automatically maintained during an experiment of many days, the reaction of the infusoria was somewhat different: they reproduced and existed not only at the pressure of 10-15 mm Hg, but also at 5 mm Hg, in an atmosphere of both air and nitrogen containing from 1 to 0.0005% O2. This indicates not only low-oxygen consumption of unicellular animals but also the capability of cells to extract some traces of this gas from the atmosphere. Low pressure and some traces of oxygen in the Martian atmosphere are not an impediment for the existence of some of the Earth's animals, such as the protozoon C. maupasi for example.

Data obtained from Mariner IV indicate that the barometric pressure on Mars is considerably lower than previously estimated. Current estimates from Mariner IV indicate a range from 4 to 7 mb and by near infrared spectroscopy 33-56 mb. Inasmuch as the pressure has a marked influence on availability of water, this should affect the existence of Martian life. At the maximum temperatures recorded on Mars, namely 25 degrees C, a barometric pressure of 30 mb is required for the retention of free water. The lower pressure, 4 mb, would suggest that the moisture is present as a vapor above the freezing point and consequently it is not available for utilizing by living cells. The lower estimates of barometric pressure also inversely affect the carbon dioxide concentration in the Martian atmosphere. Our previous studies have demonstrated that spores of Bacillus cereus survive, germinate and grow in a simulated Martian environment (2.4% CO2, 98 mb) supplemented with moisture. The studies described in this paper were designed to determine the effect of low barometric pressures (10 to 98 mb Hg) and high concentrations of carbon dioxide (37 to 100%) in the simulated Martian environment on survival and growth of B cereus. The organism was inoculated into a felsite-limonite soil at 8% moisture level. The temperature cycles used were 8 hr at -65 degrees C and 16 hr at 25 degrees C, or 20 hr at -65 degrees C and 4 hr at 25 degrees C. The data suggest that the organism after achieving maximum growth in the simulated Martian environment (2.4% CO2, 98 mb) immediately enters into the growth phase upon reinoculation into fresh soil. These data reflect upon the possibility of contamination through air movements. Based upon currently available Martian environmental data, the probability of contamination of Mars by terrestrial micro-organisms will be discussed.