Aug 24 1975
From The Space Library
A planet's size and bulk might be more important than its location in the solar system in determining whether it can support life, Dr. Robert Jastrow, Director of NASA's Goddard Institute for Space Studies, said in a New York Times article. Conventional scientific thought had always been that the chance of life's evolving on a planet was narrowly restricted by the planet's distance from its parent star. However, planetology-the study of comparative geology of the planets, made possible by space probes such as Pioneer, Mariner, and Viking-provided evidence for the newer theory.
The most important single factor in the geology of earth-like planets was the amount of internal heat left over from their birth. Planets as large as earth conserved heat, losing it very slowly through volcanic action over long periods of time. Molten volcanic material carried gases, including water vapor, that had been trapped below the planet's surface; the vapors condensed into oceans, other gases formed an atmosphere, and life began. Mariner's photos of Mars had confirmed the existence of volcanoes; but, because of the planet's relatively small size, these exhausted their internal heat supply and died out rapidly about 100 million yr ago. During its active period, Mars must have had in its atmosphere large volumes of volcanic gases, including water vapor; Mariner photos had shown what were apparently dry river beds. When the volcanoes became extinct, the water and atmosphere leaked away into space and the small planet was left dry and nearly airless. Any life forms found on Mars by Viking or future space probes would probably be fossils.
The study of lunar material added another example to the comparative geology of earth-like planets: The moon rocks brought back by Apollo astronauts had revealed volcanic activity on the moon; because the moon was smaller than Mars, this activity had stopped even earlier and the gases and moisture escaped even more quickly, leaving another dry, airless, and lifeless body.
Scientists concluded that Mars was cold and lifeless not because it was farther from the sun than earth but because it was smaller and geologically inert. If the earth were moved out to the orbit of Mars, the average temperature of the earth would drop somewhat but its insulating atmosphere, continually replenished by volcanic gases for some billions of years longer, would maintain a livable temperature over large areas of the surface. (Jastrow, NYT, 24 Aug 75, E7)
Soviet ground controllers altered the trajectory of Luna 22, the unmanned lunar probe launched 29 May 1974, bringing it closer to the moon's surface. Resulting parameters were 1286-km apogee, 100-km perigee, 3-hr period, and 21° inclination. Tass reported 3 Sept. that all onboard systems were operating well and that the spacecraft was continuing to transmit to earth information about the moon's surface. (Tass, FBIS-Sov, 3 Sept 75, U1)
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