Geomorphology of Gale Crater, Rock on! Options

[Gerald]

The "missing links" to the articles about early Mars climate:
Abstract
Full text

The other article

EDIT: For the Hesperian, I think, one should take into account the acidity of water. Sulfuric acid may decrease the freezing point of water.

[serpens]

Is the outcome of this a re-run of Nick Hoffman's white mars hypothesis? He made a good hypothetical case, but the physical and geochemical indications garnered by Opportunity over the years present compelling evidence for long lasting liquid groundwater with periodic surface exposure. As far as Curiosity's current environment is concerned I'm in the Other Doug's camp with respect to the fluvial provenance of this area. But keeping an open mind, the cementing agent in the sediment (and what appears to be significant variations in lithification) will provide a good indication of the environment in which it formed.

[dburt]

...the physical and geochemical indications garnered by Opportunity over the years present compelling evidence for long lasting liquid groundwater with periodic surface exposure. ...

That particular interpretation is still open to debate, and has already been debated extensively here and in various published articles over 5 years ago. Widespread clay minerals, reported in Gale but not Meridiani, presumably provide the best evidence for some type of liquid water or steam. The cementing agents for the weak clastic sediments visited by the first two exploration rovers on Mars appear to be various reactive, soluble salts, including acid salts - not exactly compelling evidence for persistent surface or ground water. I'll leave it at that. Please PM me if you wish clarification or a longer discussion.
- dburt

[drz1111]

I'm very sceptical of models of what climate "should" have been for early Mars. Similar models completely fail to explain the undisputed evidence for widespread liquid water, and modern-type fluvial erosion, on Hadean earth. There's a bug in our understanding of that time.

[serpens]

I share your scepticism. Given the track record of climate modellers on Earth where outcomes do not reflect predictions despite the ability to empirically measure input constants and variables, it is difficult to accept at face value the output of models directed billions of years into the past for an alien planet where many of the inputs must, of necessity, be guestimates.

[drz1111]

It's more than that. Climate models for the contemporary earth are quite good, unless we're talking about regional details not particularly relevant to an analysis of the global Mars climate. Heck, the models seem to do a pretty good job back through the entire Phanerozoic; they even can go beyond that and describe the "Snowball Earth".

But those same models can't handle the Hadean - specifically, the existence of sufficient quantities of liquid water to support modern-type sedimentary processes and/or the generation of felsic crust - based upon best estimates of insolation at that time, without some pretty improbable assumptions. And if they can't describe Earth, it's hard to imagine why they'd get Mars right. We're missing a piece of the puzzle.

[Gerald]

Pure climate models will be insufficient for a description of early telluric planets, I think. They should be extended e.g. by gravitational shrinkage heat, radioactive decay heat, impact heat, chemical reaction heat like serpentinization to become more appropriate, imho.

[Zelenyikot]

Somebody has access to the full text? Interestingly about what it.
http://www.sciencemag.org/content/338/6114/1522.1.summary

[Eyesonmars]

That was our submitted version. The in-press version is here: http://gps.caltech.edu/~kite/doc/Kite_et_al_Gale_Mound.pdf
We made several relatively minor changes in response to a useful review by Ryan Anderson, and also ran some 3D simulations as a sanity check on the assumptions in the 1D model.

Are you referring to this?

[Explorer1]

This is essentially a news article, so I'm wondering why it's behind a paywall. No matter, I have access through my university. In essence: the researchers say that since the mound's sediment layers are inclined 2-4 degrees from the horizontal (according to MRO observations), as well as the fact that none of the eroded beds reaches the crater wall, the mound is not a remnant of a sediment layer (from an old lake, say) that completely filled Gale.
Instead, they say it was primarily aeolian processes building up an enormous pile of dust. Intense winds from solar heating and air movement could have propelled its' creation from essentially nothing. Water may have been involved at some point, but only marginally.

I hope this helps.

[Zelenyikot]

Yes, thanks, for an explanation.

[Gerald]

Inclination might be a result of erosion and creeping, or a result of preferred sedimentation near the mound. Indications for clay minerals in the lower layers of Mt. Sharp still have to be explained. High D/H ratio and a high level of chemically bound water (Rocknest soil) indicate a water-rich past (Noachian) of Mars. The conglomerate finding at Curiosity's landing site strongly indicates a water-rich period. A layer in Yellowknife Bay looks much like containing bound water from the Hesperian (to be confirmed). The crater rim probably is younger as Mt. Sharp, this was assumed before. Science is an adventure; I don't feel any damper.

[Eyesonmars]

And don't forget the fairly extensive "box works".

[serpens]

The clay at the base of the mound has been identified as nontronite, indicating a wet, neutral pH environment when it formed. When Curiosity gets to the trough we should get an idea of how the smectite bearing layer formed but the extensive indications of water inflow from the rim and on the floor make a shallow lake a real possibility. Smectites consume acidity and the rate of mineral dissolution increases as the pH falls, the end product being amorphous silica. So the survival of the smectites indicates that they were protected from acid waters during the sulphate period. From Ryan Anderson and James Bell's analysis, what they term as the light toned ridge material sandwiches the nontronite layer. I guess that if it was a smectite dissolution product that would have been identifiable so it must have been impermeable.

The katabatic / slope winds hypothesis makes a lot of sense, particularly for the upper mound, but the early history seems fluvial.

[elakdawalla]

One thing I would want to check is the direction of the tilt and how that relates to the long-term changes in Mars' shape due to, say, the construction of the Tharsis volcanic complex. The MESSENGER team has shown how lava-filled craters near Mercury's pole now have tilted floors that must once have been horizontal, due to tectonic activity. My own work on Venus dealt with the same thing, measuring current topography of lava surfaces that you assume started out as flat in order to get at ancient tectonics. I'm sure the same could happen on Mars. We certainly know Mars' shape has changed in the past, and it's been suggested that the entire crust has reoriented (true polar wander). I'd love to see if the tilting observed here is consistent with geophysical work on Mars' tectonics -- or inconsistent, which would be just as interesting.