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NASA Images Suggest Water Still Flows on Mars
Guest_AlexBlackwell_*
post Dec 13 2006, 01:50 AM
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For some discussion on "alternate" theories of the gullies' formation, take this trip down nostalgia memory lane.
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AndyG
post Dec 13 2006, 09:54 AM
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QUOTE (AlexBlackwell @ Dec 13 2006, 01:12 AM) *
I haven't read or heard anyone make a connection, direct or indirect, with impact events and gully activity, though some sort of seismic activity triggering the outbursts is very plausible.

But that wouldn't address the apparent issues of disparity between sunward/shadeward facing slopes.

Andy
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climber
post Dec 13 2006, 12:14 PM
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QUOTE (AndyG @ Dec 13 2006, 10:54 AM) *
But that wouldn't address the apparent issues of disparity between sunward/shadeward facing slopes.

Andy

You're rigth Andy. Unless there's a very (improbable) narrow equilbrium. Would be important to know if brusts-gullies occure anytime during the year or more like the "geysers" at particular time of the year. Only a dedicated orbiter could address this. I wonder if there are other interests of having a regular picture (every 2 weeks) of Mars other than addressing the gullies formation. Up to last week, before the announcement, I didn't read about such a project, except for meteorological purposes. I forsee polar caps behaviour to add, landers relay, what else?


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Guest_AlexBlackwell_*
post Dec 13 2006, 04:11 PM
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QUOTE (AndyG @ Dec 12 2006, 11:54 PM) *
But that wouldn't address the apparent issues of disparity between sunward/shadeward facing slopes.

That's true, AndyG. And I should have been more precise in my reply. What I was driving at was that with only two apparent examples of recent (ca. 7 years) activity among the "thousands" of gullies, a non-insolation trigger might be plausible. I'm assuming, of course, that the putative near-surface reservoirs of liquid water do not vary temporally and spatially.
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Guest_AlexBlackwell_*
post Dec 15 2006, 05:17 PM
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Hecht and Vasavada have a new paper, "Transient liquid water near an artificial heat source on Mars," which was just published online in the open-access MARS Journal.
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JRehling
post Dec 15 2006, 06:47 PM
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QUOTE (AlexBlackwell @ Dec 13 2006, 08:11 AM) *
That's true, AndyG. And I should have been more precise in my reply. What I was driving at was that with only two apparent examples of recent (ca. 7 years) activity among the "thousands" of gullies, a non-insolation trigger might be plausible. I'm assuming, of course, that the putative near-surface reservoirs of liquid water do not vary temporally and spatially.


My long-standing suggestion here is that the sun-facing slopes don't form gullies because they would have already exhausted their reservoirs long ago, like short-period comets.

In a nutshell, a gully can form when a slope experiences something close to a meteorological record high temperature plus other factors (a little more dustpack on top of the crater) add enough stress to break the camel's back.

Seismic activity would have to be particularly well timed to have an effect.

Note that certain fault systems on Earth are more likely to experience a seismic event depending upon the tides. But obviously the overwhelming majority of tidal events (every 13 hours) do not cause quakes. It just becomes the straw that (rarely) breaks the camel's back.

Frozen rivers (such as the Nenena) break every spring when the ice melts. Presumably, a stick of dynamite well-placed on the day the ice was going to break anyway could speed the event by minutes or hours. But a stick of dynamite would not possibly cause it to break (riverwide) in January.
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Guest_AlexBlackwell_*
post Dec 15 2006, 06:56 PM
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QUOTE (JRehling @ Dec 15 2006, 08:47 AM) *
Seismic activity would have to be particularly well timed to have an effect.

An exogenic trigger for seismic activity (e.g., impact-induced) would, I agree, suffer from the dreaded "Tooth Fairy" hurdle, which I mentioned in another context.

However, it's not too much of a stretch to posit that endogenic seismic activity, assuming it occurs on Mars, could trigger outbursts. And, again, the paucity of detectable activity among the tens of thousands of sites is not an insignificant issue.
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climber
post Dec 15 2006, 08:04 PM
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There's something that make me scratch my head.
They're talking of ten of thousands gullies with only two changes in 6 years.
I can't imagine the "light tone" deposits stay for a very short period (< 6 years), so, why MGS didn't see light tone deposits at first, back in 1999?


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ustrax
post Dec 16 2006, 06:35 PM
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QUOTE (climber @ Dec 15 2006, 08:04 PM) *
There's something that make me scratch my head.
They're talking of ten of thousands gullies with only two changes in 6 years.
I can't imagine the "light tone" deposits stay for a very short period (< 6 years), so, why MGS didn't see light tone deposits at first, back in 1999?


Don't scratch...Think!
Maybe MGS catch a transition period?...
Don't you see the main bright flow getting darker and darker in a short years's period?
Mars is EX-TRE-ME-LY dynamic...


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Guest_AlexBlackwell_*
post Dec 19 2006, 12:03 AM
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The Planetary Radio interview with Ken Edgett is now online.
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Bob Shaw
post Dec 25 2006, 09:33 PM
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QUOTE (tuvas @ Dec 6 2006, 05:16 PM) *
Are you sure you can trust this source?
Is Stephen Hawking British? And MOC isn't working, let along taking a picture of Spirit... Unless....

ADDED: I guess I was wrong about Stephen Hawking. For some reason I never had thought of him as British... But he is...


Is it his accent, perhaps?

Bob Shaw


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Guest_AlexBlackwell_*
post Dec 27 2006, 09:15 PM
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Here are a couple of new martian gullies-related papers in press with Icarus:

Martian gullies in the southern mid-latitudes of Mars: Evidence for climate-controlled formation of young fluvial features based upon local and global topography
Icarus, In Press, Accepted Manuscript, Available online 23 December 2006
James L. Dickson, James W. Head and Mikhail Kreslavsky
PDF (724 Kb) (Subscription required)

Comparison of small lunar landslides and martian gullies
Icarus, In Press, Corrected Proof, Available online 21 December 2006
Gwendolyn D. Bart
Abstract

For non-subscribers, click here for more information on Gwen Bart's work (scroll down for links to her martian gullies work, which was presented at LPSC earlier this year).

As for Dickson et al., you may also wish to keep an eye on the Brown University Planetary Geosciences Group publications page. I suspect the paper will be available there fairly soon.

This post has been edited by AlexBlackwell: Dec 27 2006, 10:21 PM
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Guest_AlexBlackwell_*
post Jan 3 2007, 09:43 PM
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I just noticed a new paper in press with Icarus:

Observations of Martian Gullies and Constraints on Potential Formation Mechanisms, Part II: The Northern Hemisphere
Icarus, In Press, Accepted Manuscript, Available online 3 January 2007
Jennifer L. Heldmann, Ella Carlsson, Henrik Johansson, Michael T. Mellon and Owen B. Toon
PDF (1253 K) (subscription required)

I believe this is a companion piece to an earlier paper in Icarus by Heldmann and Mellon [2004]. For those without access to Icarus, here is a (715 Kb PDF reprint).

By the way, in case anyone wants to wade through a master's thesis on this particular aspect of martian gullies research, see Nina Lanza's submission earlier this year in May 2006 to Wesleyan University: "Geometries of martian hillside gullies in the northern hemisphere: evidence for an insolation-driven mechanism of formation" (8.01 Mb PDF).

This post has been edited by AlexBlackwell: Jan 3 2007, 10:01 PM
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climber
post Jan 6 2007, 02:51 AM
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At first this topic included the discovery of recent craters and as I don't know other place to post this message, I post it here.
I didn't realise that, from MGS observations, the rate of formation is one crater per MONTH. Whoua, that's a lot. They also said that is you stay in the same place for 20 years, you'll be close to one impact. Vicking landers have been there for much longer. Does somebody know if the location of the fresh craters has been released?


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nprev
post Jan 6 2007, 04:07 AM
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Glad you mentioned this, Climber; been wondering about the implications for landing/settlement.

The big question seems to be whether the amount of risk incurred for surface installations on Mars is significantly above the Earth background level. Our atmosphere conveniently disposes of many otherwise dangerous meteors, but will we have to deeply bury any future Martian colonies? huh.gif


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