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Lunar and Planetary Science Conference 2001 - Part One
Cameron Park - May 1, 2001 The 32nd Annual Lunar and Planetary Sciences Conference -- held in Houston from March 12 through 16 -- like all the LPSCs before it, was a major scientific powwow at which scientists from the world over presented hundreds of papers and posters on the geology, meteorology and chemistry of the other worlds and objects in our Solar System, from giant planets down to meteorites. As always, many of the papers (especially those dealing with the detailed geochemical analysis of meteorites and returned Moon samples) were so specialized and dry in their subject matter that they hold appeal only for fellow scientific specialists, and/or masochists -- but as always, many were of great interest to anyone with a reasonable degree of interest in the exploration of other worlds. As to be expected a major theme of this year's LPSC was the ongoing debate as to just how much liquid water Mars had on or near its surface during its earliest days, and how much it has now. The relevance of this to the question of whether ancient Mars had microbial life -- and even whether Mars may still have some, buried deep beneath its savagely hostile present-day surface -- is obvious. And the debate is still as furious as ever. Back in 1996, when the MGS spacecraft first entered orbit around Mars and began the first really detailed close-up scientific survey of the planet since the Viking missions, the single most popular model of the planet's history -- what might be called the "Modern Classic" view -- ran as follows. During the first billion or so years after its creation -- the so-called "Noachian" period -- Mars had a carbon dioxide atmosphere that was belched from out of its early volcanoes, to provide a far denser atmosphere than its faint wisp today. Indeed, its surface air pressure may have been as much as present-day Earth's, or perhaps even several times greater. One major piece of evidence for this is the fact that craters dating back to that epoch are much more eroded than all the craters existing on areas of Martian land which (judging by their sparser total crater count) were volcanically resurfaced after the Noachian era -- indeed, these oldest craters are so much more eroded as to indicate that only wind erosion in a genuinely dense atmosphere could have done it. And one consequence of that dense CO2 atmosphere would have been a powerful greenhouse effect -- strong enough to warm much of Mars' surface above the freezing point of water.
Some researchers, however, think they see subtler signs that Noachian Mars had a lot of liquid water on its surface -- everything from grooves in some of Mars' southern highlands that may have been gouged by glaciers created by accumulated snowfall on its mountains, to features around the edge of the great lowland depression taking up most of Mars' northern hemisphere which just might be the shorelines of an ancient ocean that once filled that lowland (which is also floored with plains of material so extremely flat that they may be seafloor sediment). And this is just the sort of environment in which microbial life might very well have evolved on ancient Mars at about the same time it was first evolving on Earth. However, Mars -- unlike Earth -- then gradually lost that early dense atmosphere. Some of it -- because Mars' gravity is so much weaker than Earth's -- may have been splashed into space by the huge asteroid impacts which were still common in those early days of the Solar System.
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The best evidence for this is the scattering of ancient "valley networks" across the planet -- which look very much like branching dry riverbeds, and were almost surely formed by the flow of a moderate amount of some fluid across the surface over long periods of time.
