Watering Mars with volcanism
The role of water may not be the ultimate question in the study of the planet Mars, but it is an essential factor in understanding the answer(s). Was Mars once wetter? Warmer? More earth-like? It is a vastly complicated problem, from the amount of water originally present within the planet to the quantities that remain today in such diverse reservoirs as permafrost, hydrated minerals and perhaps even subterranean aquifers of liquid.
Various estimates of the total volume of water on Mars have been based on such factors as the distribution of elements throughout the solar system, studies of certain meteorites believed to have come from Mars, examination of what appear to be water-carved "outflow channels" on the Martian surface and more. Few of these studies, however, says Ronald Greeley of Arizona State University in Tempe, have dealt with the amounts and timing of water released from the planet's interior in the course of its evolution.
Some of the water would have been present since the planet's formation, but much would have formed later on in association with volcanism, the evidence of which is visible in thousands of the photos taken by the two Mars-orbiting Viking spacecraft. Greeley estimates in the June 26 SCIENCE that volcanism could have acconted for the equivalent of a ater layer 46 meters deep over the entire planet. (Previous water estimates, he says, not confined to the role of volcanism, have ranged from 1 meter to 1 kilometer.)
In 1979, he and a colleague concluded from the Viking photos that volcanism has "resurfaced" more than 41 percent of the Martian surface, by their best estimate, and that the total could be as high as 64 percent (SN:11/10/79, p.329). Recently prepared global geologic maps based on the Viking data, says Greeley, still indicate that materials apparently of volcanic origin cover more than half the surface.
Constructing a panorama of Martian water history from such a finding, however, is a formidable task. …