[X] My Assistant

[Chmee]

What is everyone's thoughts on origin of the smooth low-lands on Mars and why they are so different from the cratered high-lands?

I beleive there are at least three theories:

1. The low-lands are the result of a super-large impact on the Northern hemisphere (during the Noachian age). This impact erased the earlier craters leaving the low, smooth surface seen today.

2. The low lands were cratered just as the highlands were, but later (Amazonian) hemisphere-wide lava flows erased all evidence of the craters.

3. The low lands were cratered just as the highlands were, but an early ocean laid deposits in this low- area, burying the earlier craters.

I am leaning towards both theory 1 and 2. In other words, a very early impact on Mars created the dichotomy we see now on Mars (by basically blasting a large proportion of teh Northern Hemisphere completely away) but later hemisphere-wide lava flows filled in this low lying area.

Thoughts?

[Guest_BruceMoomaw_*]

There's another LPSC abstract that deals with the ice question. They aren't even finding such minerals in the areas where Phoenix will land -- which consist of just a few cm of soil spread over solid ice: http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1706.pdf .

So as the OMEGA team says, Mars has been devoid of any large amount of surface liquid water for a VERY long time. Presumably non-hydrated soils have indeed covered the northern plains for that very long time -- but they must cover any existing hydrated Fe oxides, phyllosilicates, or sulfates very deeply indeed, because all of those are being seen in just a few tiny patches on the Martian surface exposed by the chance patterns of erosion. And Mars Express cannot analyze from orbit any substance buried by more than a fraction of a cm of other material -- I can't think of any instrument that CAN do so except for gamma-ray and neutron spectrometers.

Finally, those local magnetospheric bubbles do absolutely nothing to provide shielding against solar UV (or, for that matter, X-rays and neutrons) -- just against solar charged particles. And their shielding against those isn't all that intense. As far as I know, there is absolutely no correlation between them and the exposed patches of hydrated minerals. (In fact, another LPSC abstract -- which I can't track down at the moment -- compared the highest-intensity magnetic "stripes" found by MGS with local mineral maps made by the various orbiters, and found no compositional correlation with that either. Whatever minerals are responsible for the stripes are also deeply buried.)