Earthlike Mars? Options

[glennwsmith]

All, I know this isn't the right place for this post, but I've looked around and can't find an appropriate, current UMSF forum (Doug, perhaps you could give me some guidance on establishing such) -- so here goes: I think a [the] new paradigm for Martian geology is rapidly coalescing, namely, that Mars is very much like the Earth in terms of the preponderance of water -- except that it is all frozen, and covered under a thin layer of dust/regolith! See, for example, this article:

http://www.skyandtelescope.com/news/41995902.html

Hence the "seepages" found in crater walls; hence the evidence of catastophic flooding -- the result of volcanism melting huge pockets of ice. And I am going to add my own wrinkle (probably not original): that the differentiation of Mars into a rougher southern hemisphere and smoother northern hemsphere represents something like Earth's Pangea stage, ie, the northern hemisphere is a vast frozen sea covered with a thin layer of ice.

[dburt]

... I think a [the] new paradigm for Martian geology is rapidly coalescing, namely, that Mars is very much like the Earth in terms of the preponderance of water -- except that it is all frozen, and covered under a thin layer of dust/regolith! .... Hence the "seepages" found in crater walls; hence the evidence of catastophic flooding -- the result of volcanism melting huge pockets of ice. And I am going to add my own wrinkle (probably not original): that the differentiation of Mars into a rougher southern hemisphere and smoother northern hemsphere represents something like Earth's Pangea stage, ie, the northern hemisphere is a vast frozen sea covered with a thin layer of ice.

Doug, thanks for moving this. And Glenn, not a particularly new paradigm for many scientists. Everyone wants to emphasize similarities with Earth, but you have spotted a major difference - that the water is all or mostly frozen. This has been speculated on for a long time; it's nice to find direct proof. Freezing/sublimating the water released all the salts that were held in solution; both rovers, plus orbiting satellites are continually finding more salts. Another difference is the extreme age of the martian crust - billions of years, owing to an apparent lack of plate tectonics on Mars since then (implying the comparison with Earth's Pangea stage may not be an appropriate one). The ancient crust has preserved the record of ancient Martian impact cratering much better than on Earth; even the hemispheric division of Mars has been blamed (by many scientists) on a giant impact.

Incidentally, the northern hemisphere is just as heavily cratered as the southern one, except that it is lower-lying, and so the ancient craters are mostly buried under a thin layer of dust and ice, as that article pointed out. Orbital studies involving detailed elevation and radar have allowed the northern buried craters to be detected (see numerous articles by Herbert Frey). The very thin atmosphere means that impact cratering is still a far more important process than on Earth - small meteorites do not burn up in the atmosphere. A final difference from Earth is that the martian crust and lavas are at least twice as rich in iron as on Earth - an important difference that probably relates to the initial degree of hydrogen loss (core oxidation) during the formation of Mars. In part, this iron-rich nature accounts for the rusty red color of Mars - and presumably accounts, in some fashion, for the prevalence of shiny gray hematite (iron oxide) spherules at the Opportunity landing site.

The big scientific question regarding Mars now is not its water-rich nature, but rather how much of, and for how long, this water might have remained liquid, rather than frozen, on ancient Mars, during and just after ancient impact cratering episode that ended about 3.8 billion years ago (age assumed from dating of Moon rocks sampled during the Apollo astronaut program). I find it easiest to relate abundant evidence for early liquid water to the impact cratering episode itself (an easy way to generate lots of heat, a temporary steamy atmosphere, and layered sediments resembling those seen by both rovers), but others prefer to relate liquid water to early volcanism, an unusual and dense atmosphere, or both. Impacts and volcanism are not mutually exclusive, of course - both were occurring at at a high rate at roughly the same time, and afterwards both continued at a greatly reduced rate.

-- HDP Don