Here Be Dragons

HERE BE DRAGONS
disproved the existence of life at the locations they examined. And because
the wind on Mars tends to blow surface dust around the planet,
it was hard to see how life could exist anywhere on the surface without
producing some kind of a positive result at the two landing sites.
There were suggestions that living creatures still might be found in
some unexplored niches, such as the polar caps or possible hydrothermal
springs, but the general effect of the Viking mission was to bring
the notion of life on Mars to a low point of credibility.
Curiously, however, the Viking mission also held the seeds of a rebirth.
While the landers were conducting the biology experiments, the
two orbiters carried out a detailed photographic survey of Mars. It was
the results of this survey, combined with the earlier Mariner data, that
opened a new debate—one that is still raging—about the possible existence
of life on Mars in some past epoch, when the planet was
warmer and wetter than it is today.
"Basically, it boils down to a very simple argument," says McKay.
"All the conditions on Earth that have been postulated to be critical to
the origin of life have also existed on Mars. Hydrothermal systems, organics
coming from comets, sunlight for photosynthesis, sulfur-rich
CO 2 [carbon dioxide] chemical systems like Wachtershauser looks at.
Whatever theory you like, I'll make it work on Mars. Water Yes,
3.8 billion years ago, when life had already appeared on Earth, water
was flowing on Mars."
McKay brings out a picture that looks, at first glance, like a photograph
of Earth as seen from the Moon: a sphere hanging in the blackness
of deep space, with a ruddy continent set off by clouds and by the
engirdling blue of a vast ocean. "I used this in an article for Astronomy
magazine," he says. "It's a real case of a picture worth a thousand
words. I show this to a general audience and say 'Mars may have
looked like this once. This is not just a fantasy.' " 6
To make his ocean, McKay relied heavily on the work of Michael
Carr, a planetary geologist at the United States Geological Survey at
Menlo Park, a few miles north of Moffett Field. 7 Carr has made a close
study of what appear to be water-carved features on Mars's surface.
The most spectacular of these features are the "outflow channels,"
many of which are found in the region around the Chryse Basin in
Mars's northern hemisphere, just to the east of the towering volcanoes
of the Tharsis Highlands.
The outflow channels were formed when highly pressurized subter-
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