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Tom Tamlyn
A new paper argues that HiRISE photos show evidence for recent short-lived surface water flows. Neat pictures on Phil Plait's site (my source for the news).

It would be interesting to learn if there was any MGS coverage of the same area.

TTT
schaffman
These gully-like features in Russell crater were described by Nicholas Mangold and others in 2003 using MGS MOC and MOLA images:
Mangold, N.; Costard, F.; Forget, F. (2003). Debris Flows over Sand Dunes on Mars: Evidence for Liquid Water. J. Geophys. Res., 108(E4), 5027, doi:10.1029/2002JE001958.
Michael Carr also discusses them briefly in his book The Surface of Mars, 2006.

Tom

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Tom Tamlyn
Thanks!
tharrison
QUOTE (Tom Tamlyn @ Apr 12 2010, 01:12 PM) *
It would be interesting to learn if there was any MGS coverage of the same area.


There are a number of MOC narrow-angle images of the Russel dune gullies as the area was monitored for change. MSSS put out a few captioned image releases of them:

http://www.msss.com/mars_images/moc/2003/04/27/index.html
http://www.msss.com/mars_images/moc/2005/05/08/index.html
http://www.msss.com/mars_images/moc/2005/11/05/
ilbasso
Say, were you guys the victims of those pranks in high school, too?

Oh, sorry. I thought this topic was More Wet Willies.
Paolo
on arXiv today: Martian gullies: Produced by fluidization of dry material
tharrison
QUOTE (Paolo @ May 3 2010, 10:15 AM) *


Someone has started a separate thread about this paper: http://www.unmannedspaceflight.com/index.p...ic=6584&hl=
Dysgraphyk
A new paper showing recurring dark streaks.
Nature comments : "Water seems to flow freely on Mars"

McEwen, A. S. et al. Nature Geosci. http://dx.doi.org/10.1038/ngeo2014 (2013).

QUOTE
River-like valleys attest to the flow of water on ancient Mars, but today the planet is dry and has an atmosphere that is too thin to support liquid water on the surface for long. However, intriguing clues suggest that water may still run across the surface from time to time.

In 2011, for example, researchers who analysed images from NASA's Mars Reconnaissance Orbiter (MRO) spacecraft observed dark streaks a few metres wide that appeared and lengthened at the warmest time of the year, then faded in cooler seasons, reappearing in subsequent years2. "This behaviour is easy to understand if these are seeps of water," says planetary scientist Alfred McEwen of the University of Arizona in Tucson, who led that study. "Water will darken most soils."

The streaks, known as recurring slope lineae, initially were found at seven sites in Mars's southern mid-latitudes. The water may have come from ice trapped about a metre below the surface; indeed, the MRO has spotted such ice in fresh impact craters at those latitudes.

McEwen and his colleagues have now found the reappearing streaks near the equator, including in the gargantuan Valles Marineris canyon that lies just south of it. The MRO has turned up 12 new sites each of which has hundreds or thousands of streaks within 25 degrees of the equator. The temperatures there are relatively warm throughout the year, says McEwen, and without a mechanism for replenishment, any subsurface ice would probably already have sublimated.

He says that this suggests that water may come from groundwater deep in the crust (...)

But even though McEwen says that water is the most likely explanation for the streaks, he is not sure of the sources. Some of the streaks seem to begin at the tops of ridges, too close to the surface to easily be explained by subsurface aquifers. So the water may come instead from atmospheric water vapour that is pulled into salts in the soil and later released.

"It is quite difficult to understand how [the streaks] can occur with the current understanding of Mars," says Gerhard Kminek, vice-chair of COSPAR's planetary protection panel and planetary protection officer at the European Space Agency. "And that makes it more interesting of course."


source : Nature news
nprev
Interesting idea, but still a long way from proof.

I often wish for an orbiter capable of capturing events in real-time, not only for this phenomenon but also for the landslides in the polar regions, dust devils, etc. What seem to be dynamic processes are much easier to understand if you catch them in the act.
0101Morpheus
Maybe NASA should land the next rover near a gully to clear it up.
ngunn
Well, we already have a rover sniffing for organics in retreating scarps. Maybe it will also find ice subliming there and not just minerals with a lot of water of crystallisation. On the other hand the water in the gullies could come from the breakdown of hydrated minerals rather than melting ice.
serpens
Breakdown of hydrated minerals on the polar side of dark, probably basaltic dunes at temperatures no higher that say 20 celcius for a brief period? What hydrated minerals are you proposing or are you thinking minerals in frozen brines?
Phil Stooke
I can't yet see these features as anything but dry granular flows. I'm willing to be shown I am wrong...

Phil

Gerald
QUOTE (serpens @ Dec 13 2013, 01:49 AM) *
Breakdown of hydrated minerals on the polar side of dark, probably basaltic dunes at temperatures no higher that say 20 celcius for a brief period? What hydrated minerals are you proposing or are you thinking minerals in frozen brines?

The only hydrated mineral with that property I know of is meridianiite decomposing in epsomite and water. This should be possible to distinguish from basalt, i.e. confirmed or discarded.
nprev
Again, speed of propagation is a critical parameter which we are currently not well equipped to measure.
marsbug
QUOTE (Phil Stooke @ Dec 13 2013, 12:59 AM) *
I can't yet see these features as anything but dry granular flows. I'm willing to be shown I am wrong...

Phil

I'm more or less of the same mind: I don't see any specific reason why they shouldn't be caused by some kind of brine...but I see no reason why they should be, brine just being one of a great many alternative explanations. I think this story is really riding in the wake of the discovery of ancient habitable conditions at Curiositie's site.
algorimancer
QUOTE (marsbug @ Dec 13 2013, 05:57 AM) *
... I don't see any specific reason why they shouldn't be caused by some kind of brine...but I see no reason why they should be, brine just being one of a great many alternative explanations. ...

Agreed. This may be troublesome to sort-out. Even given remote measurements of associated water vapor, I could envision a dust-fall yielding a water vapor release due to the exposure of subsurface ice/brine, rather than being directly associated with a liquid seep. It seems we would need to image actual flowing water to resolve this, and I think even MRO lacks that level of resolution.
marsbug
I stumbled across this on the bbc science and technilogy site: Water carved gullies on Vesta? I'm just bringing it up to make the point: Features that are very suggestive of a water like fluid occur even on worlds where the idea of ANY liquid surface water strains the imagination.
TheAnt
QUOTE (marsbug @ Dec 15 2013, 05:18 PM) *
Features that are very suggestive of a water like fluid occur even on worlds where the idea of ANY liquid surface water strains the imagination.


Funny that you mentioned that one, since I have used those features on Vesta as one example that the gullies on Mars must have been done by the same kind of flow. Saying that it in both cases must be extremely dry dust that without any trace of humidity (causing stickiness) creating flows that resemble one made by a liquid.
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