Mars is fascinating to scientists and science fiction writers, not because it is exotic, but because it is so much like Earth, with so much to teach us about ourselves.
Mars has a solid, rocky surface. It has an atmosphere. It has clouds, seasons, fog, frost, winds and dust storms. There are icy polar caps and probably a frozen ocean of water hidden beneath its barren landscapes.
In short, the place has all the raw materials needed to support a good sci-fi plot, or real life. Maybe it has supported life of its own. Maybe it could support us.
But as scientists at NASA and in Russia prepare this week for the start of Earth's most ambitious robotic exploration of the Red Planet, it is the search for Martian water that holds center stage.
Where there is water, said Wesley F. Huntress, who heads NASA's office of space science, "there is always the potential for life having arisen on Mars, and having survived there."
Answering that question in the affirmative could settle one of mankind's oldest mysteries: Are we alone in the universe?
Water could also supply the needs of explorers. They could breathe it [Mars' carbon dioxide atmosphere is thin and unbreathable], drink it, or break it down into hydrogen and oxygen -- handy rocket fuel for the trip home.
Hopes of finding life on Mars faded in 1976 when NASA's twin Viking missions found no chemical traces of it on the planet's barren surface, where temperatures average 64 degrees below zero Fahrenheit.
In the 20 years since, however, scientists have found life in some very inhospitable places on Earth -- in Antarctic cold; around blistering hot thermal vents in the dark, crushing depths of the ocean; and miles deep in the Earth's crust.
Geologists studying Viking photographs have also found clear evidence that Mars once had abundant liquid water, and therefore warmer temperatures and a thicker atmosphere -- all preconditions to the evolution of life as we understand it. They see remnants of ancient lake shores, deeply carved river channels and broad outwash plains -- all now dry.
NASA's Mars Pathfinder mission will land July 4 at a place in the Martian "tropics" called Ares Vallis, about 525 miles southeast of the Viking I landing site.
Dr. Michael Carr of the U.S. Geological Survey said Ares Vallis is an ancient flood plain formed by a catastrophic release of water. It is similar to the Channeled Scabland region of Washington, where a glacial dam broke thousands of years ago and released a volume of water equal to that in Lake Erie and Lake Ontario in two weeks.
An international team of 60 scientists settled on the site because such a deluge would have washed down the widest possible variety of upland rocks for Pathfinder's rover to study.
But "where is that water now?" Carr asked. While some may have escaped into space, he said, there is "abundant evidence" that much remains beneath the Martian surface as rock-hard frozen ground water. Geologists see places where there has been glacier-like movement of surface material, and they suspect those rocks are mixed with ice.
It may be possible, scientists say, that primitive life did evolve on Mars billions of years ago, much as it was evolving on Earth. Then, as Mars' climate grew colder and drier, perhaps Martian organisms evolved and adapted, retreating to hydrothermal systems near its volcanoes, or the warmer, wetter depths of its crust. The fossil microbes NASA scientists think they saw on a Martian meteorite last summer look like deep-rock bacteria found on Earth.
Perhaps Mars still has such microbes and future missions could be designed to find them. Perhaps life was extinguished on Mars by global climate change.
Some scientists believe Mars may hold important lessons about the forces that can push a planet's climate beyond its ability to sustain life.
Or maybe Mars has never known life. We may be alone after all.
Pub Date: 11/05/96