[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?

[dvandorn]

OK -- first off, are you saying that MEX is finding no sign of hydrated iron oxides in the very soils that seem to be giving off a fair amount of hydrogen, as detected by Odyssey, and therefore are assumed to be covering significant ice deposits? Or at least that contain a significant admixture of ice?

So, which set of readings do we believe -- the ones that show a lack of hydrated iron oxides, or the ones that indicate a significant ice presence within much of this region?

If there is ice in close proximity to the surface of the northern portion of the northern hemisphere, how can that ice exist within and under soils that show no signs of hydration? And if the soils were emplaced after the ice was emplaced, then the non-hydrated soils could be covering an ancient sea floor and MEX wouldn't have a clue.

Another point -- is MEX looking at the very surficial layer, which may be dust and soils generated from non-hydrated basalts dating from the Tharsis development, or does it "see" deeper than the very surface layer? Is it possible that non-hydrated dust deposition may have covered any hydrated iron oxides that might still lie rather close to the surface?

And finally, is there any correlation between the places where MEX sees hydrated iron oxides and those places where the erratic magnetic field seems to be shielding the surface from solar UV? If you want to test UV effects, and if you can assume that these erratic magnetic "loops" that form bubbles of partial UV screening are long-lived, then it makes sense to identify these areas as precisely as possible and then compare surface characteristics inside and outside of them...

-the other Doug