Adv. SpuceRes. Vol. 15, No. 3, pp. (3121l-(3)214, 1995 Copyright0 1994 COSPAR Printedin GreatBritain.All rightsreserved. 0273-l 177/95 97.00 + O.UU
STUDIES IN THE SEARCH FOR LIFE ON MARS
J. Koike,* T. Oshima,* K. Kobayashi** and Y. Kawasaki***
* Tokyo Institute of Technology, 4259 Negatsuta, Yokohama 227, Jupan ** Yokohama National University, Hodogaya, Yokohama 240, Japan ***Mitsubishi-kasei Institute of Life, Machida, Tokyo 194, Japan
ABSTRACT The ability of living organisms to survive extraterrestrial conditions has implications for We have therefore studied the survival of viruses, the origins of life in the solar system. The environment on Mars was and fungi under simulated Martian conditions. bacteria, yeast, ultraviolet irradiation, and simulated simulated by lowtemperature, proton irradiation, After Martian atmosphere (CO2 95.46%, N2 2.7X, water vapor 0.03%) in a special cryostat. tobacco mosaic virus and spores of Bacillus, Aspergillus, exposure to these conditions, and some species of coccus showed significant survival. Clostridium, INTRODUCTION we have been studying survival rates of terrestrial In connection with planetary quarantine, If common terrestrialorganisms cannot organisms under simulated space conditions /l-7/. we can reduce expenditure for sterlization of space survive in space for even short periods, probes, but if terrestrial organisms can survive for significant periods under such conprecautions will be necessary to prevent other planets in our solar system from di tions, In 1975, the Viking becoming contaminated with terrestrialmicroorganisms and microfloras. mission to Mars carried experiments specifically designed to search for signs of microbial life on Mars. The results suggest that biological activity was not present at the landing sites, but provide convincing evidence that liquid water was present on early Mars and that atmospheric pressure and temperature were considerably higher than at present /S-10/. If is itnecessarily now extinct? What kind life did evolve on Mars at some time in the past, Although present conditions on plars are of life can survive under Martian conditions /ll/? not at all favorable to terrestrial life forms, what kind of terrestrial microbes might be able to survive there, and for how long? MATERIALS AND METHODS Equipment The low-temperature and high-vacuum cryostat attached to anion-pumped vacuum system and Van de Graaff accelerator is shown in Fig. 1. The sample is cooled by liquid nitrogen and heated by the heater. Liquid nitrogen is supplied from the top of the device and stored in the tank. The inner cylinder can slide up or down. By means of movement up into proximity with the liquid nitrogen or down toward the heater, the temperature of the sample could be controlledeasily and quickly between 100 and 500°K under high vacuum conditions and was measured by the thermocouple. The chamber was evacuated to 1 x 10d8 torr by an ion vacuum were prepared from a hexagonal copper cylinder and rotated as necessary pump- Sample holders by neans of the upper handle to bring each face in turn into the path of the proton stream. Samples of microorganisms were attached to thefaces of the sample holders. The slit through which the proton stream entered the cryostat was 20 mm wide. The beam of proton particles from the Van de Graaff accelerator was bent by an analyzing magnet and collided with the sample holder in the cryostat. In this study, the mean energy of protons was adjusted to 1 MeV, and the electric current was 0.01-0.05 nA. The intensity of protons was monitoredby a measure of the electrons liberated when the protons collided with the sample holder. Ultraviolet radiation was also applied to the sample by a vacuum H2-lamp. Experimental Conditions
Organisms were exposed to two different simulated Martian environments. For simulation of conditions under the Martian atmosphere, samples were exposed to the conditions listed under the “laboratory” column...
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