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Lunar and Planetary Science Conference 2001 - Part Seven
Cameron Park - May 1, 2001 In short, this year's LPSC papers on Mars make it abundantly clear that a new paradigm has become extremely important in understanding the strange and puzzling history of Mars: the idea that the planet's geology has been radically affected by the fact that -- unlike Earth -- it's cold enough for great amounts of carbon dioxide to get into its subsurface. It now seems likely that many Martian surface features that have previously explained as being due to liquid water may really be due to CO2 -- indeed, it's conceivable, though unlikely, that all of Mars' "water-carved" features are really due to it. While Nick Hoffmann has probably been the most important figure in advocating this new picture of Mars, he's not the only one. Others -- including Jeffrey Kargel, Kenneth Tanaka and D.S. Musselwhite -- have also become strong advocates of it at about the same time. But the new papers also make it clear that as of now, where Mars is concerned, we're still in the position of the six blind men trying to understand the elephant -- we still don't have enough pieces of the puzzle, to get a clear understanding of Mars' overall history. MGS and the Mars orbiters that will follow it will continue to map more of Mars' surface at very high resolution -- the 2005 U.S. "Mars Reconnaissance Orbiter", in fact, is scheduled to photograph large portions of Mars with a resolution of only 30 cm, and spew the photos back to Earth at rates of up to 4 million bits per second. But it seems very likely now that pictures of Mars' geological features alone won't be enough to solve its puzzle. In particular, we need one very important piece of the puzzle: analyses of Mars' surface minerals, to see whether they are indeed the types formed by interactions with large amounts of surface liquid water, or whether they indicate instead that the planet's surface has always been dry and perhaps has reacted chemically with CO2 instead. Our mineralogical data on Mars, unfortunately, is still rudimentary -- the thermal-IR mineral maps from MGS have been limited in the information they have provided us, and the three successful Mars landers so far have just measured the percentages of different elements in the surface, which doesn't tell us much about the actual chemical compounds those elements have formed. As I noted earlier, perhaps the most unfortunate aspect of the loss of Mars Polar Lander is that its TEGA instrument would have given us a surprisingly detailed mineralogical analysis of Mars' soil, to look for just such water-formed minerals -- and since Mars' soil has been pretty evenly mixed all over the planet by dust storms, this could have given us an idea of how wet the entire planet's surface has been during its history. The upcoming Mars orbiters will also try to make much better mineralogical maps of Mars than MGS has done. The just-launched Mars Odyssey has a multispectral thermal-IR camera which has less spectral resolution than MGS, but far sharper resolution than MGS' fuzzy 2-km resolution mineral maps -- if carbonates exist on Mars' surface only in small outcrops, it may be able to find them. The 2003 European Mars Express will give us our first map of Mars in shorter-wavelength "near-IR" -- which can detect a different set of minerals -- and the 2005 U.S. orbiter will follow up by making near-IR maps with a resolution of only 50 meters. But they may be less useful than hoped. The disappointing mineralogical blandness of Mars in MGS' mineral maps may be explained by the fact, reported at the Conference by T.G. Graff, that his studies show that the long-wavelength "thermal IR" radiation it measures penetrates a thin film of dust on rocks less effectively than had been thought -- and virtually all of Mars' rocks are covered by such a thin layer of uniformly mixed windblown dust (as confirmed by A.T. Basilevsky's new analysis of the findings from Mars Pathfinder). If so, then the shorter-wavelength near-IR radiation to be measured by future orbiting spectrometers will have even more trouble penetrating that dust, and be less informative. It's starting to look as though the only way to make good chemical analyses of different places on Mars may be to send multiple landers down to scrub the dust layer off local rocks and analyze them directly.
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