Life?

In the mid-1970s, NASA launched the Viking spacecraft to Mars. Each included an orbiter and a lander, and one of the main purposes of the landers was to search for life. First, of course, you have to define what life is in order to know how to search for it. Astronomer Carl Sagan (a noted planetary scientist and host of the 1980 PBS series, COSMOS) hoped that Vikings’ cameras would see what he called a "macrobe" walking by in front of it. He even argued for a flashlight on the lander, so that any nocturnal life form galumphing by might also be captured on camera! Most scientists pinned their hopes on experiments designed to look for "microbes"--tiny life forms too small to see with cameras. Viking’s robotic arm would reach out and scoop up soil and drop it into a series of chambers. One test would feed the sample with liquid nutrient, and see if anything resembling Earth-like reactions happened, a sign that biology was present. Another test looked for the organic molecules which enable life on our own Blue Planet. Amazingly enough, one of these experiments did return data which by criteria established before launch seemed to indicate life! But the other tests didn’t confirm that finding, and most researchers now think it was some exotic chemistry, not life, which produced the ambiguous result: others still think Viking may have found signs of life.

While the Viking landers didn’t clinch the case for life, most planetary astronomers were amazed by what the orbiters showed us. All over the planet there were channels which seemed to have been carved by liquid water. There were tear-drop shaped islands which resembled those shaped by Earth’s rivers. Even if life didn’t clearly show its presence, Mars did seem once to have had plentiful liquid water, and researchers had begun to realize that here on Earth life seems to exist just about anywhere liquid water is present. So despite the confusing experimental results, the Viking missions did, in fact, encourage researchers and the public to think that life might once have existed on Mars.