September 21, 2007 | David F. Coppedge

Mars Was and Is Dry

The cover story of Science this week has bad news for those hoping for Martian lakefront property.  A series of articles by planetary scientists who studied images from the Mars Reconnaissance Orbiter casts strong doubt on the presence of water on Mars, even in the planet’s early days.  The overview article by Richard Kerr in Science1 summarizes:

In recent years, “water, water everywhere” might have been the motto for Mars exploration.  Shallow, salty seas ruled on early Mars, and water has been gushing down gullies in the geologically recent past, some even in the past few years.  But the tide is now receding, at least a ways.
    As highlighted in the 21 September issue of Science and elsewhere, more leisurely consideration of observations from rovers and orbiters and the unprecedented detail afforded by Mars Reconnaissance Orbiter (MRO)–the latest arrival at Mars–are bringing into question many earlier geologic interpretations involving surface water.  Mars has been “a desolate place for a long time,” concludes geochemist Scott McLennan of Stony Brook University in New York state.

Leading Marsologists, like Alfred McEwen (U of Arizona), contributed to the series of five papers in the issue.  It appears that volcanic activity can account for the layered deposits, and slumping can account for the apparent gullies on crater walls.  Joanne Baker summarized the way the evidence is looking now, in her introductory article, “Water, Water, Not Everywhere?”2

Images of supposed ancient ocean floors and riverbeds show no obvious signs that liquid water was ever present.  Reexamination of some landforms implies that they have been formed by flowing lava, not water.  The only locations where features seem to indicate the presence of liquid water today or in the recent past are on the rims of craters and some gullies, suggesting that heat from impacts may have been the trigger for trickles rather than a revealed water table.  Radar and gravity data show that the cap on Mars’ south pole now holds the largest reservoir of relatively pure water ice on the planet, and layers there and in the north polar cap reveal seasonal oscillations in climate.

This represents a major blow to previous ideas about the red planet.  The Mars Pathfinder rover was thought to have landed in a large, ancient flood channel.  The Mars Exploration Rovers looked long and hard for water; Spirit was supposed to have landed in a flooded lake bed, which turned out to be volcanic debris, but Opportunity seemed to have provided evidence for intermittent shallow seas.  The new evidence is casting doubt on all those visions.  We now may have to work with a revised picture of Mars as a dry, dusty, rocky desert, with wandering icy polar caps, where liquid water has only flowed in rare, ephemeral trickles.

1Richard A. Kerr, “Is Mars Looking Drier and Drier for Longer and Longer?”, Science, 21 September 2007: Vol. 317. no. 5845, p. 1673, DOI: 10.1126/science.317.5845.1673.
2Joanne Baker, “Water, Water, Not Everywhere?”, Science, 21 September 2007: Vol. 317. no. 5845, p. 1705, DOI: 10.1126/science.317.5845.1705.

This must be a severe disappointment to origin-of-life researchers.  The motto “follow the water” has driven much of the Mars program.  Mars remains just as fascinating a geological body as it always was, but with decreasing hopes for water, and therefore life, will there be enough wind in NASA’s sails to keep going back?
    Phoenix is on its way to a polar landing next year.  The mission overview clearly states that water ice and organic compounds necessary for life are a prominent goal of the mission.  The Mars Science Laboratory, scheduled to rove the planet in 2010, has even more experiments to “collect Martian soil and rock samples and analyze them for organic compounds and environmental conditions that could have supported microbial life now or in the past.”  Today’s papers in Science may begin to decrease hopes for even past life.  Will NASA scientists be able to keep Mars plans vibrant beyond MSL, when the goals stated for Mars Beyond 2009 are heavily influenced by Astrobiology?  How much will scientists want to study lava and dust in more detail?
    We hope planetary exploration will continue apace.  Here’s a replacement goal that creationists and intelligent design people (i.e., the majority of taxpaying Americans) can support: “We learn from exploring other planets and moons just how special our Earth is, and how narrow are the requirements for life that are met uniquely on the home planet.”  There’s potential for a lot of good science with that focus.  Astrobiologists can even continue to look for life.  The more they don’t find it, the more we will appreciate how special life is.  Everybody wins.  We will not cease from exploring, T.S. Eliot said.  When we come back home, we will understand the place for the first time.  That’s worthwhile.
    Scientists must face things as they are, not as they wish them to be.  Did you notice that the earlier claims of liquid water were apparently due to the eagerness to find it?  Kerr said that only after a more “leisurely” look at the observations did the dry truth begin to sink in.  That’s not all bad.  Science is often driven by the eagerness to prove or disprove something.  As long as scientists are honest when their hunches don’t bear up, worthwhile findings can result.  We’re only human, though, and emotions do get involved.  It’s a good thing Percival Lowell (Mr. Martian canals) is dead, because he would be sooooo depressed.  But look: his eagerness bequeathed to us the Lowell Observatory.

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