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search for extraterrestrial life within the solar system and throughout the universe. Philosophical speculation that there might be other worlds similar to ours dates back to the ancient Chinese and Greeks.
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the scientific discipline devoted to the study of life in the universe in all its forms. Astrobiology is based on scientific achievement in the areas of astronomy, biology, and biochemistry. In solving certain problems, astrobiology is intimately connected with space biology and space medicine, disciplines which arose along with man’s active penetration of cosmic space.
An important problem in astrobiology is the study of the circumstances of the origin and development of life on earth as a cosmic body under primordial terrestrial conditions in the presence of a basic atmosphere. In such an atmosphere fairly complicated organic compounds, which might have served as the basis for the development of life, could have formed in the presence of external irradiation or electrical discharges. Gradually this life could have formed an extensive biosphere, whose cosmic role has been indicated by V. I. Vernadskii. As a result of the photosynthesis carried on by plants, the earth’s atmosphere gradually became oxidized; thus, the presence of oxygen in the composition of the atmosphere of any planet is a sufficient (though not an obligatory) indication of the presence of life on that planet.
Scientific information about the physical nature of the various planets obtained up to the middle of the 20th century testifies to the fact that life is not possible on every body in the solar system. In particular, it has been established that life is practically impossible on the moon, on Mercury, and on Venus. On Mars, in spite of its extremely rarefied atmosphere (absolute pressure of the order of 1 kilonewton/m2, that is, 10 millibars), the negligible quantity of water vapor in the absence of liquid water, and the low temperature (-55° C on the average), certain terrestrial forms of life could still exist, as has been demonstrated in laboratory experiments. However, a definitive solution of the problem of the existence of life on other planets can be reached only by the direct inspection of these planets by the appropriate space vehicles. The flights of the American Apollo spaceships confirmed the conclusions of astrobiology about the absence of life on the moon. Advances in astronautics permit one to hope that the solution of this problem with regard to the other bodies in the solar system is also near. Projects for experiments devised to discover life on other bodies with the help of automatic apparatus are based on the assumption that life on these planets has the same hydrocarbon basis as on earth. Life organized on another basis (ammonia, silicon) is not very likely. The major argument in favor of the universality of life on a hydrocarbon basis is that, as is shown by the detailed study of the primordial meteoritic matter (carbonaceous chondrites), the formation of extremely complex hydrocarbon compounds (anthracene, phenanthrene, and even the basic elements of deoxyribonucleic acid—the purine bases adenine and guanine) could have taken place in the preplanetary stage in the primordial gas-dust nebula; later this organic material became part of the planets as they formed, and under favorable conditions it determined the development of life on these planets.
A special problem of astrobiology concerns the search for life outside of the solar system. A significant number of stars in our galaxy could have planets with the appropriate circular orbits, sufficient masses, and constant irradiation suitable for the existence of life and even of civilizations. The number of such civilizations with a higher level than that on earth is estimated on the basis of various (sometimes considerably arbitrary) assumptions to be from about 1,000 to hundreds of millions. However, even in the latter case, only one such star out of many hundreds would be located at a distance of the order of 10 or even 100 parsecs (1 parsec = 30.86 x 1012 km) from the earth. Therefore, it is completely unrealistic, for the present, to think of sending any kind of spaceship into galactic space to establish direct contact with extraterrestrial civilizations. The establishment of contact with other civilizations with the aid of radio signals is more realistic. Such attempts to establish contact with possible civilizations near the stars τ Ceti and ∊ Eridani (distance of 3.9 and 3.5 parsecs), which could be presumed to have planetary systems, were begun by F. Drake (USA) in 1960 at the Green Bank Radio Observatory; positive results have not been obtained. In order to establish such contact, it is necessary to choose correctly the direction of signal emission, the length of the radio waves, the content of the broadcast, and the code. These problems are being studied in many scientific institutions in the USSR, the USA, and other countries.
REFERENCESLiubarskii, K. A. Ocherki po astrobiologii. Moscow, 1962.
Shklovskii, I. S. Vselenndia, zhizn’, razum, 2nd ed. Moscow, 1965.
Mezhzvezdnaia sviaz’. [A collection of articles, edited by G. W. Cameron.] Moscow, 1965. (Translated from English.)
Firsoff, V. A. Zhizn’vne Zemli. Moscow, 1966. (Translated from English.)
Ursul, A. D. Osvoenie kosmosa. Moscow, 1967.
Vnezemnye tsivilizatsii. Edited by S. A. Kaplan. Moscow, 1969.
V. G. FESENKOV