National Geographic : 1973 Feb
But the information from Mariner 9 begins to throw a new light on these hazards. For example, the discoveries of volcanism and of the riverbeds on Mars indicate, as we have seen, that the planet may have had a substan tial supply of water that at intervals became available in liquid form. And perhaps in the very lowest parts of Mars, where the atmosphere is denser and therefore exerts more pressure, water from melting permafrost might linger below the surface or perhaps even briefly on the surface. Another possibility is shown by infrared spectra that suggest huge amounts of water on Mars bound up in minerals of the soil perhaps a thousand times as much as in the atmosphere. This is not liquid or frozen water, but the same water of crystallization or absorption that we find in earth rocks. Could this water be available to living things on Mars? Dr. Harold P. Klein thinks it might be. "I don't know of any organism that can pull water out of a crystal on earth," he told me, "but perhaps there is an analogy with the halophiles, or salt-loving bacteria. These are pink or purplish creatures that live in salt water and can be seen in large numbers at the edges of bays. Some species cannot grow unless they have at least 20 percent salt in their environment. "I don't see why Mars could not have evolved organisms that could adapt equally well to extreme situations. If water gradually became scarce, they could have worked out ways to extract water from minerals." As far as free oxygen is concerned, some lower forms of life on earth do not need it. In the early history of earth, oxygen was absent from the atmosphere or present only in small amounts. Oxygen was probably at first poi sonous to earthly life, and for some organisms still is. The bacillus that causes tetanus, for example, cannot grow in the presence of oxygen. So perhaps Martian organisms would not need free oxygen. ULTRAVIOLET radiation is a some what different problem, because it is hard to conceive of Martian organisms that would not be damaged by ultraviolet, if it reached them. But several protections seem possible. Dust in the air would reduce ultra violet during storms. Similarly, Mars likely has plenty of iron bearing silicates in its soil, and perhaps or ganisms there have evolved silicate shells like those of diatoms, tiny algae in the sea, with ultraviolet-blocking pigments. It is important to remember that life on earth has developed to accommodate to the terrestrial environment. In the billions of NASA Black and battered, Mars' two tiny moons reflect the wear of billions of years of mete orite bombardment. Phobos (left and page 230), a craggy oval 17 miles long, speeds around the planet twice each Martian day. Deimos (above), only 10 miles long, is the solar system's smallest known satellite. In a fleeting solar eclipse, Phobos throws its shad ow on Mars (far right), 4,000 miles away.