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In the early flush of excitement about the landing and the first photographs, none of the Viking scientists seemed particularly disappointed that the pictures showed no obvious signs of life—no lichen, bushes or trees, nothing even remotely resembling an animal or the monsters or little green men beloved by generations of science-fiction writers. Said Exobiologist Carl Sagan: "The pictures do not suggest that the planet is filled, pole to pole, with living things." But, noted Sagan, nothing in the pictures ruled out the existence of life on the planet either. Soffen added that the lander's immediate vicinity held half a dozen niches in which conventional biology, including hundreds of life forms, could be detected in a desert on earth. "The microbes of Mars are within our grasp, if they are there," said Soffen. "There could be cockroaches under those rocks."
Indeed, Mars seems to possess many of the elements essential to life on earth. Most of Mars' visible water appears in the form of atmospheric vapor or ice locked in the planet's two polar caps (the surface pressure on Mars is so low* that liquid water would probably boil away). But liquid water apparently once did flow freely on the Martian surface in earlier days; Viking's orbital pictures show that the planet is crisscrossed by dry "riverbeds" and sinuous valleys, including a deep Grand Canyon-like depression called the Valles Marineris, that were probably carved out by running water. During Viking's descent, the lander's instruments sniffed and measured both nitrogen (3%) and argon (1.5%) in the Martian atmosphere. Nitrogen is an essential element in the molecules of terrestrial life. Also, the presence of approximately the same percentage of argon found in the earth's air suggests that Mars at one time had a denser atmosphere more conducive to the evolution of life. Said Dr. Michael McElroy, a Harvard University physicist: "At an early stage. Mars apparently had enough pressure to hold quantities of water." And even today, notes the scientist, Mars may be capable of supporting life. "Look at what we need for life," said McElroy. "We need water; that we have. We need nitrogen; that we have. Phosphorus, phosphates ... I see no reason to exclude, from every thing we know, the possibility of the evolution of life Ion Mars]."
Between now and mid-November, when Mars passes behind the sun and communications with earth are cut off, Viking's two cameras will take regular photographs of Chryse Planitia, observing what takes place throughout each Sol, or Martian day, of 24 hr. 37 min. Other instruments, meanwhile, will sample the contents of the Martian atmosphere, register the planet's temperatures, which range from a low of -200° during darkness to a high of +50° during the day, and record wind velocities, barometric pressures and humidity. A seismograph, placed aboard the Viking to detect Marsquakes and volcanic activity, was apparently not working at week's end, but scientists still had hopes that they could coax it into operation.