An Odyssey of Mars Science: Part 3

Martian H20 Deposits as mapped by NASA's Mars Odyssey orbiter

by Bruce Moomaw
Sacramento - Feb 12, 2004

The new data from Mars Odyssey's GRS and THEMIS instruments, of course, are also providing information on some aspects of Mars that have nothing to do with the amount of liquid water that may have existed on its surface -- and William Boynton and Phil Christensen, during their lectures on the subject at the DPS meeting, mentioned these too.

Hydrogen isn't the only element in the upper third of a meter of Mars' surface measured by Mars Odyssey. Its gamma-ray spectrometer is making increasingly good maps of the distribution of oxygen, silicon, iron, potassium, thorium and -- most recently -- chlorine on the surface, with a peak resolution of about 300 km. In the near future, the researchers also hope to start making maps of several more elements. Once again, these have opened up new questions.

First, there's the mystery of why the 29 "SNC" meteorites that have been pretty firmly identified as being chunks of Mars rock -- thanks to several factors, including the traces of identifiable Martian atmosphere trapped inside them, their internal exposure to modest amounts of water, and the relatively recent dates at which most of them last solidified out of lava -- don't match our new surface composition maps of Mars at all well, in either the gamma-ray or the infrared wavelengths.

The spectra made by Mars Global Surveyor's "TES" medium-wavelength infrared spectrometer already indicated that most of Mars' exposed rocks fall into two general categories: "Type 1 and 2". Type 1, which makes up most of the highlands that cover Mars' southern hemisphere, seems to be basalt -- while the Type 2 rock which dominates the lowlands making up most of Mars' northern hemisphere seems to be much richer in silica (silicon dioxide). It may be either the more silica-rich volcanic rock "andesite", or else water-weathered basalt which has developed a thin surface crust of silica which TES is detecting.

But ut the TES spectra of neither rock matches the recovered Mars meteorites at all well. They are a different form of basalt, even poorer in silica and also lacking the aluminum-rich mineral "plagioclase feldspar" which seems much commoner in both the Type 1 and Type 2 rocks.

The rest is here: http://www.spacedaily.com/news/lunarplanet-2003-03c1.html>/a>