The earliest simulation studies were carried out by the Air Force, and the studies during the past 6 years have been supported by NASA. Recently, these studies have received less support or have been terminated in favor of critical studies on the effects of biologically important environmental extreme factors on Earth organisms. These critical studies permit establishing the extreme environmental factor parameters in which Earth life can grow or survive. These data will have valuable application to the consideration of life on any planet, to the design of life-detection instruments, to the sterilization of space vehicles, and to the problem of contamination of planets.
Some exploratory experimental studies are in progress to study the capabilities of organisms to grow under the assumed conditions on Jupiter. These include studies at high pressure with liquid ammonia, methane, and other reducing compounds.
Early experiments simulating Martian conditions using soil bacteria were carried out by Davis and Fulton ([ref.70]) at the Air Force School of Aviation Medicine, San Antonio, Tex. Mixed populations of soil bacteria were put in "Mars jars" with the following conditions: 65-mm Hg pressure, 1 percent water or less, nitrogen atmosphere, sandstone-lava soil, and a temperature day-night cycle of +25° to -25° C. The moisture was controlled by desiccating the soil and adding a given amount of water. Experiments, conducted up to 10 months, demonstrated that obligate aerobes died quickly. The anaerobes and sporeformers survived. Although a small increase in the total number of organisms indicated growth, the increases in the number of bacteria may have been due to breaking up clumps of dirt.
Roberts and Irvine ([ref.71]) reported that, in a simulated Martian environment, colony counts of a sporeforming bacterium, Bacillus cereus, increased when 8 percent moisture was added. Moisture was considered more important than temperature or atmospheric gases inasmuch as a simulated Martian microenvironment containing 8 percent moisture permitted germination and growth of endospores of Clostridium sporogenes. Increases in colony counts of Bacillus cereus appeared to be influenced by temperature cycling ([ref.72]).
| Species | Survival, months | Moisture | Temperature, °C | Atmospheric pressure, mm Hg | N2, percent | CO2, percent | Substrate |
|---|---|---|---|---|---|---|---|
| Conditions on Mars: | 14µ±7µ | -70 to +30 | 85, 25±15, 11 | 3 to 30 | |||
| Anaerobic sporeformers Clostridia, Bacillus planosarcina | 6 | Low, (CaSO4) | -60 to +20 | 76 | 95 | 5 | Air-dried soil |
| Anaerobic nonsporeformers Pseudomonas, Rhodopseudomonas | 6 | Low, (CaSO4) | -60 to +20 | 76 | 95 | 5 | Air-dried soil |
| Anaerobes Aerobacter aerogenes, Pseudomonas sp. | Growth | Very wet | -75 to +25 | 760 | 100 | (?) | Difco infusion broth |
| Clostridium, Corynebacteria "Thin short rod" | 10 | 1 percent or less | -25 to +25 | 65 | 100 | (?) | Soil |
| Bacillus cereus | 2 | 0.5 percent soil | -25 to +25 | 65 | 94 | 2.21 | Sandstone soil |
| Clostridium sporogenes | 1 (growth) | 8.4 percent | -25 to +25 | 65 | 94 | 2 | Enriched soil |
| Clostridium botulinum | 10 | Lyophilized | -25 to +25 | 65 | 95 | 0 to 0.5 | Lava soil |
| Klebsiella pneumoniae | 6 | Lyophilized | -25 to +25 | 65 | 95 | 0 to 0.5 | Lava soil |
| Bacillus subtilis var. globigii | 4 | 2 percent | -25 to +25 | 85 | 95 | 0.3 | Media |
| Sarcina aurantiaca | 4 | 0.5 percent | -25 to +25 | 85 | 95 | 0.3 | Desert soil |
| Clostridium tetani | 2 or less | 1 percent | -60 to +25 | 85 | 95 | 0.3 | Soil |
| Aspergillus niger | Over 6 hr | Very dry | -60 to +25 | 76 | 95.5 | 0.25 | Glass cloth on copper bar |
| Aspergillus oryzae | Over 6 hr | Very dry | -60 to +25 | 76 | 95.5 | 0.25 | Do. |
| Mucor plumbeus | Over 6 hr | Very dry | -60 to +25 | 76 | 95.5 | 0.25 | Do. |
| Rhodotorula rubra | Over 6 hr | Very dry | -60 to +25 | 76 | 95.5 | 0.25 | Do. |
| Pea, bean, tomato, rye, sorghum, rice. | 0.3 | Moist | +25 | 75 | 100 | 0 | Filter paper |
| Winter rye | 0.6 | Moist | -10 to +23 | 76 | 98 | 0.24 | Soil |
Studies of the effects of simulated Martian environments on sporeforming anaerobic bacteria were carried out by Hawrylewicz et al. ([ref.49]). They showed that the encapsulated facultative anaerobe, Klebsiella pneumoniae, survived under simulated Martian atmosphere for 6 to 8 months, but were less virulent than the freshly isolated organisms. Spores of the anaerobe Clostridium botulinum survived 10 months in the simulator. Hagen et al. ([ref.53]) found that the addition of moisture to dry-simulated Martian soil did not improve the survival of Bacillus subtilis or Pseudomonas aeruginosa. Bacillus cereus spores survived, with added organic medium plus moisture, but no germination of the spores resulted.
Hawrylewicz et al. ([ref.49]) put rocks from Antarctica bearing various lichens in simulated Martian conditions in a large desiccator. They found that the algal portion of a lichen, Trebouxia erici, showed only slight resistance to the Martian environment. They also pointed out the effect moisture had on the physical condition of lichens. The undersurface of a lichen has great water-absorbing capability, and the slightest amount of moisture on a rock surface is absorbed by the lichen which can turn green in 15 minutes.
Scher et al. ([ref.51]) exposed desert soils to simulated environmental conditions and diurnal cycles of Mars. The atmosphere consisted of 95 percent nitrogen and 5 percent carbon dioxide (no oxygen) and was dried, using calcium sulfate as a desiccant. The total atmospheric pressure was 0.1 atm. The temperature ranged from -60° to +20° C in 24-hour cycles. One hour was spent at the maximum and at the minimum temperatures. The chambers were irradiated with ultraviolet, 2537 Å, with a dose of 109 ergs/cm2, which is comparable to a daily dose found on Mars, and easily exceeds the mean lethal dose for unprotected bacteria. Soil aliquots were removed weekly and incubated at 30° C. The scoring was done both aerobically and anaerobically. Sporeforming obligate and facultative anaerobes, including Clostridium, Bacillus, and Planosarcina, and nonsporeforming facultative anaerobes, including Pseudomonas and Rhodopseudomonas, were found. The experimental chambers were frozen and thawed cyclically up to 6 months. Organisms that were able to survive the first freeze-thaw cycle were able to survive the entire experiment. The ultraviolet irradiation did not kill subsurface organisms, and a thin layer of soil served as an ultraviolet shield. All of the samples showed survivors.
Young et al. ([ref.52]) assumed that water is present on Mars, at least in microenvironments, and that nutrients would be available. The primary objective of their experiments was to determine the likelihood of contaminating Mars with Earth organisms should a space probe from Earth encounter an optimum microenvironment in terms of water and nutrients. The experiments used bacteria in liquid nutrient media. The environment consisted of a carbon dioxide-nitrogen atmosphere, and the temperature cycling was -70° to +25° C, with a maximum time above freezing of 4½ hours. Aerobacter aerogenes and Pseudomonas sp. grew in nutrient medium under Martian freezing and thawing cycles. Atmospheric pressure was not a significant factor in the growth of bacteria under these conditions.
Silverman et al. ([ref.47]) studied bacteria and a fungus under extreme—but not "Martian"—conditions. Spores of five test organisms (B. subtilis var. niger, B. megaterium, B. stearothermophilus, Clostridium sporogenes, and Aspergillus niger) and soils were exposed while under ultrahigh vacuum to temperatures of from -190° to +170° C for 4 to 5 days. Up to 25° C there was no loss in viability; at higher temperatures, differences in resistivity were observed. At 88° C, only B. subtilis and A. niger survived in appreciable numbers; at 107° C, only A. niger spores survived; none were recoverable after exposure to 120° C. B. subtilis survived at atmospheric pressure and 90° C for 5 days, but none of the other spores were viable alter 2 days. Four groups of soil organisms (mesophilic, aerobic, and anaerobic bacteria, molds, and actinomycetes) were similarly tested in the vacuum chamber. From one sample only actinomycetes survived 120° C, while one other soil sample yielded viable bacteria after exposure to 170° C. Several organisms resisted 120° C in ultrahigh vacuum for 4 to 5 days. When irradiated with gamma rays from a cobalt 60 source, differences were observed between vacuum-dried spores irradiated while under vacuum and those exposed to air immediately before irradiation. A reduction of from one-third to one-ninth of the viability of spores irradiated in vacuum occurred with vacuum-treated spores irradiated in air.