Mars Explained... I think.

I just had a paper come out in Nature Geoscience about the sediments at Meridiani Planum -- please go and see it. The abstract is the following:

The sulphate-rich deposits at Meridiani Planum, Mars, discovered by the rover Opportunity, were proposed to be playa evaporites that had been reworked by eolian processes. Alternative hypotheses include volcanic or impact-driven formation of the sediments. Here we argue that the cation chemistry, scale, mineralogy and structure of the Meridiani sedimentary deposits are best explained by eolian or impact-driven reworking of the sublimation residue from a large-scale deposit consisting of dust and ice. We suggest that silicate material underwent significant acid weathering inside the ice deposit when thin films of water, formed through radiant heating, enabled the reaction between silicate material and sulphate-rich aerosols deposited from the atmosphere. The massive ice deposit could have formed during a period of high obliquity or polar wander, and subsequently sublimed away when obliquity changed or the pole moved to a new location. We propose acid weathering inside massive ice deposits as an explanation for the formation of many of the sulphate-rich layered deposits on Mars, which share many characteristics, including mineralogy, structure, erosional characteristics and size, with the sediments found at Meridiani Planum.

So with that introduction, my grand unified theory of Mars, at the risk of coming out half-baked or maybe even a quarter-baked:

1. In the first couple hundred million years of Mars' history (perhaps shorter) conditions on Mars were probably very different from today, the planet had just accreted, I imagine there was a fair amount of chaos. The question is whether or not this period featured any significant aqueous alteration that we can see today. This hinges on whether or not significant water was present on the surface, and not boiled away by impacts, volcanism, or just not degassed from the interior yet. I'm going to posit that the extensive phyllosilicates detected in ancient crustal rocks are from this period -- but I've got another couple of possibilities later on.
2. As things calmed (and cooled) down the next question is whether there was a thick atmosphere -- and how long it lasted. My argument is that if there was a thick atmosphere it was not long lived (not more than 100 million years or so), it was lost to space through impact events, stripping by solar wind, etc.. My reasons for thinking this are that we don't see well developed fluvial features, I don't think evidence for an ocean is strong, there are not extensive carbonates or other evaporite deposits from this period we've found (Please read above for Meridiani).
3. I think Meridiani is really the key for understanding the conditions during this period. Most important in my mind are the constraints posed by the chemistry and mineralogy. We've got a deposit of silicates that have been completely altered by aqueous alteration but show no fractionation in cation composition from a basalt. This indicates that it was weathered in a closed system -- a low-water-rock ratios.
4. So we've got a planet where there are fluvial features, ice deposits, and the like, which all require some sort of recharge. But we don't have enough CO2 to account for a warmer climate and rainfall. Instead we have a planet which undergoes huge obliquity variations through time which serve to redistribute the ice from the poles to the equator. This could be the recharge mechanism we are looking for. And if this ice-weathering idea proves to be feasible, we can explain sulfate formation as well.
5. Outflow channels -- require huge volumes of water, repeated surges. But their source regions aren't large basins with many tributaries leading into them -- they are just relatively small chaos terrain. So we have giant channels that require massive floods but no obvious source that's big enough. Ice seems to meet this requirement as it would sit on the surface and provide a massive source -- it also has the tendency of creating large floods.
6. Layered Terrain -- This includes interior layered deposits (ILD's), crater mounds, as well as plains deposits (meridiani-type). The idea here (not original of course) is that layered terrain closely resembles polar layered deposits and formed from the same mechanism. It is though polar layered deposits are a result of obliquity variations. One issue is reworking - and this is what needs work - some of these deposits would preserve their original layering -- even though ice has sublimed away (perhaps ice still exists in the cores of these ILD's and crater mounds?), others would be reworked by aeolian, impact, and fluvial processes. Can we tell the difference?
7. Valley networks -- Might be related to basal melting of obliquity ice deposits. I find it interesting that they are generally located on an equatorial band.

I think that pretty much captures it for water on Mars. Comments anyone?

Update: Check out the article at space.com