A question here, behaviour of water on Mars Options

[spdf]

A question here

There are signs that in the past there was liquid water on Mars. So lets assume thats true.
Since the gravity on Mars is much lower than on Earth, so how does water (waves) behave on Mars compared to Earth?
Someone did say, that waves would have been much higher but also much slower. Is this true? Does anyone have an animation where you can see a waive on Earth in comparsion to a wave on Mars?

Thanks

[Juramike]

Space.com article says that the crust of Mars is colder (and thicker) than previously thought.

From the article:

"Unexpectedly, the radar scans also revealed the massive weight of the ice cap does not deform any underlying sediment. This implies the crust beneath the cap is strong — more than 180 miles thick (300 km).

To have such a thick crust, "Mars might be colder than we thought," Phillips told SPACE.com. As a result, any liquid water that might be underground has to be buried even deeper than once speculated. "If one thought that liquid water was 5 kilometers deep (3 miles), it's now at least 30 percent deeper than that," he said."

(The article to be published in the May 15 issue of Science is not yet available.)


I have a really ignorant question, here: What is the ductile strength of sediment with interstitial ice? Is it stronger or weaker than normal sediment?

-Mike

[dburt]

Space.com article says that the crust of Mars is colder (and thicker) than previously thought.

From the article:

"Unexpectedly, the radar scans also revealed the massive weight of the ice cap does not deform any underlying sediment. This implies the crust beneath the cap is strong — more than 180 miles thick (300 km).
..."

I have a really ignorant question, here: What is the ductile strength of sediment with interstitial ice? Is it stronger or weaker than normal sediment?

Mike - So here's an ignorant answer. If by "normal sediment" you mean unconsolidated sediment (i.e., loose particles) where the pore space is filled with liquid water (below the water table) or air (above the water table), presumably ice-cemented sediment should be somewhat stronger, because ice is a solid. However, ice expands as it freezes, and can move sedimentary particles around (e.g., in ice polygons inferred on the Martian surface), so that ice-cemented sediment could be weaker than an actual sedimentary rock (if the particles in the rock were cemented by something stronger than ice).

That ambiguous answer may be irrelevant, though, because the space.com quote appears to be inadvertently misleading. They are not really talking about deformation of a thin, weak sedimentary veneer, but about deformation of the much stronger and thicker underlying igneous (metamorphic?) crust and uppermost olivine-rich mantle (i.e., what geophysicists call the lithosphere on Earth). The colder the underlying solid rock, the less easily deformable it is. So what they are mainly saying, if I am guessing correctly, is simply that Mars is somewhat more rigid (and therefore colder by inference) inside than was formerly modeled (at least beneath the poles). Calling this cold, rigid layer "the crust" appears to be PR-speak for "cold and rigid lithosphere". The present-day lack of plate tectonics on Mars (i.e., the fact that Mars is a one-plate planet) already implies that Mars has a very thick, rigid, non-deformable lithosphere. The lack of deformation owing to the weight of polar ice caps strengthens (pardon the double-entendre) this inference. Again, just my ignorant answer - I'm not a geophysicist and haven't read more than what you quoted. (I do know enough to state that a seismic network on Mars could provide badly-needed data about the martian interior.) Hope this clarifies rather than confuses.

-- HDP Don

[Juramike]

Hope this clarifies rather than confuses.
-- HDP Don

Yup. I asked the wrong question by using the wrong terms.
Hopefully, now I can ask better questions:

What is a good estimate for the water content of Martian lithosphere compared to Earth?
In deep crustal rocks, would this be as "free" water or would most of it be incorporated into hydrated minerals ?
How would the lithospheric water (free or hydrated minerals) content affect rigidity? Does it matter what form it would be in (liquid or frozen?)?

-Mike

[dburt]

...What is a good estimate for the water content of Martian lithosphere compared to Earth?
In deep crustal rocks, would this be as "free" water or would most of it be incorporated into hydrated minerals ?
How would the lithospheric water (free or hydrated minerals) content affect rigidity? Does it matter what form it would be in (liquid or frozen?)?

Mike - I'm writing this from home, so this is completely off the top of my head, but I'm not sure there's any really good basis at this point for estimating the water content of the martian lithosphere. You'd need lots of well-characterized samples, and all we have now is a few martian meteorites from undocumented sources. My impression is that the deep lithosphere, given that melting it generally produced (produces?) olivine-rich basalt, was/is relatively dry, even more so than on Earth. This is consistent with the very localized hydration seen along fractures in the Martian meteorites - evidence of local, relatively brief exposure to brines, at least in those samples. No wholesale hydration (as in greenschist- or greenstone-type, or serpentinite-type metamorphic rocks formed on Earth via wholesale hydration of basalt and mantle rock, respectively) has yet been detected, AFAIK. Hydrated minerals commonly include phyllosilicates (layer-structured clays and micas), which tend to be somewhat slippery (e.g., talc or "soapstone") and so wholesale hydration would be expected to produce a mechanically weakened rock (unless it consisted of say, higher temperature amphibolite, a stronger rock).

As for the state of water in the deep lithosphere, the big question would be how deep? Where the crust is below or close to the freezing temperature of water, the amount of hydration would be small, owing to kinetic limitations, even if much free water or ice or concentrated brine were present in fractures. Once things got "hot" or even "warm" hydration should be more common, if abundant liquid (or supercritical fluid) were present. The apparent strength of the martian lithosphere might then imply that it is very cold, very dry, or both (and probably not very highly hydrated). Given that ice is much weaker than most rocks except rock salt (as implied by, e.g., its flowing in glaciers) the deep martian lithosphere, even if it is sufficiently cold, is probably not particularly rich in ice (let alone liquid water). The prevailing opinion is that if there's a lot of water on Mars, it probably lies mainly near the surface, in the highly broken regolith that resulted from meteorite bombardment, mainly as ice (with perhaps some highly concentrated brine). The low atmospheric pressure currently keeps it from appearing at the very surface, except ephemerally or at the poles. Again, just off the top of my non-geophysicist head - corrections welcomed.

And dvandorn - that's was a good observation about the Tharsis pile of volcanic rocks. I completely neglected to mention that. Thanks.

-- HDP Don