[X] My Assistant

[Guest_AlexBlackwell_*]

Water May Not Have Formed Mars' Recent Gullies
By Lori Stiles
University of Arizona News Services
March 16, 2006

[ljk4-1]

"Are Martian Gullies Generated by Granular Flows?" by Dr. Troy Shinbrot of Rutgers University.

An Associate Professor of Biomedical Engineering at the New Jersey institution, Shinbrot's regular area of study is how various pharmaceutical products flow and interact with each other.

At a conference he co-organized with Cornell Professor Michel Louge in 2002, Shinbrot was discussing the "beautiful pictures" he saw of the Martian gullies. To Shinbrot, these surface features looked like they were made by the sandy particles themselves moving down the sides of banks, canyons, and craters, and not by liquid water.

...

From his previous granular flow research, Shinbrot knew that very light particles in a lower gravity environment act like a liquid before they eventually settle together to behave as regular solids.

Full article here:

http://www.zwire.com/site/index.cfm?newsid...id=216620&rfi=8

Dr. Shinbrot's Web site:

http://sol.rutgers.edu/~shinbrot/NewHome2006/index.html

[JRehling]

I'll insert here a post I made four years ago in another forum:

<< As I tumbled over the dunes in Death Valley yesterday morning
(remaining afoot, however, which I did NOT do on the salt playas at the
lowest point in the Western Hemisphere -- OUCH!), I noticed several
interesting phenomena in the sand that my footfalls inadvertently
triggered.

When I stepped at the top edge of a incline, this often
precipitated a downslope flow of sand, sometimes of surprising volume.
Quite simply, the "vertical" surface of a sand dune is in equilibrium,
but only barely, and some of those surfaces took very little to push
them over the edge to instability.
The morphology was also interesting. Quite often, the flow
followed a V shape. However, as I watched the flows form, I noticed a
beautiful and surprising dynamic -- the flows did not always form top-
first, bottom-later. Often, the initial flow (from the top) caused
lower portions along the trail to erode to the point that the vertical
layers above them (nearer where the flow began) lost their support from
below, and then I saw a beautiful wave head UPHILL at about 1 m/s. This
was not the movement of material uphill, but the spreading of a
secondary wave of collapse. Visually, it almost seemed as though the
initial event started a downward flow that then bounced upwards; a
point midway down the slope would first experience an initial flow of
sand from above to below, then, after being quiescent for a while
(during which the wave moved on), it would undergo a second collapse,
brought on by the loss of support from below, and leading to the
subsequent collapse of the portion of the slope immediately above it,
in an upward domino effect.

Pertaining to the martian gullies, I make these poor attempts at
an Archimedean analogy:
1) Did the gullies REALLY form top to bottom, or vice versa? Could
the collapse of a small point in a barely-stable layer just below the
gullies lead to a V-shaped excavation in the gully layer, causing our
attention to go to the wrong layer?
2) If the slopes in question are just barely stable, and near the
state of equilibrium, could we probe their formation by performing a
Deep Impact sort of concussion? This may be costly to bring about, but
it would be nice to have a lander looking up at a slope waiting for
concussive events that we know are coming, and seeing what flows
result. Obviously, not practical in the near term...
3) In a bit of half-empty/half-full reasoning... It seems that all
the theorizing on the gullies supposes that an event is occuring which
actively propels material downward. However, with the vertical slopes
near equilibrium, is it also not possible that a very subtle LOSS of
stability could trigger a landslide? Rather than delivering an actual
shock, couldn't the trigger event be a slight weakening of materials
that are just barely holding their weight? Perhaps due to eons-old
frost sublimating just a little more than they already had?
>>

Alex had some interesting answers to my points, which I won't insert here without permission.

[tty]

From his previous granular flow research, Shinbrot knew that very light particles in a lower gravity environment act like a liquid before they eventually settle together to behave as regular solids.
http://sol.rutgers.edu/~shinbrot/NewHome2006/index.html

Was the research conducted on the Moon? As far as I know it is the only "lower gravity" environment ever visited by humans.

tty

[ljk4-1]

Was the research conducted on the Moon? As far as I know it is the only "lower gravity" environment ever visited by humans.

tty

No, aboard NASA parabolic flights (the Vomit Comet) as I recall.

The papers on his Web site may have the details.

http://www.pnas.org/cgi/content/abstract/101/23/8542

[Guest_AlexBlackwell_*]

"Are Martian Gullies Generated by Granular Flows?" by Dr. Troy Shinbrot of Rutgers University.

Note that Shinbrot et al. published their work in 2004 in the Proceedings of the National Academy of Sciences.

See also

Treiman, Allan H.
Geologic settings of Martian gullies: Implications for their origins
J. Geophys. Res. Vol. 108 No. E4
10.1029/2002JE001900
08 March 2003
Abstract

Alex had some interesting answers to my points, which I won't insert here without permission.

No problem, John. Go ahead. If I don't like it, I can always plead lack of memory (à la Moomaw).

[Bob Shaw]

There are all sorts of funny physical mechanisms which might be at work on Mars, and a granular flow, complete with standing waves and the rest, is entirely feasible. But, and it's a biggie, when you have a crater wall, or valley side, where the same mechanism begins (or ends) at exactly the same point in the strata then it's a big hint that there's something about that particular layer which is causing the effect. OK, it might well not be water flow in the Earthly sense, but I'd still put my money on H20 being in there!

Bob Shaw

[JRehling]

No problem, John. Go ahead. If I don't like it, I can always plead lack of memory (à la Moomaw).

I'll repost the info in two installments in this post, each of which includes another post by quotation:

I wrote, quoting Alex:
--- In planetary_sciences@y..., "alexblackwell_2000" <ablackwell@c...>
wrote:
> --- In planetary_sciences@y..., "jarehling" <rehling@c...> wrote:
>
> > The morphology was also interesting.
>
> Did you by chance notice any anastomosis or channel piracy, which is
> observed at the Malin and Edgett gully sites and which is also a
> characteristic of subaerial fluid flow (as opposed to a dry mass
> movement) moving down a topographical gradient under the influence of
> gravity?

No, I didn't. In the case of the dunes, the flows I was looking at
were too small (decimeters wide, a meter long) to show some of the
phenomena that might have shown up on a larger scale.
You seem to suggest that the observed morphology of martian
gullies is incompatible with dry mass movement (with the following
caveat:)

> FWIW, though, Allan Treiman of LPI posits in an abstract
> ("Dry Mars: Parched Rocks and Fallen Dust") from the NASA
> Astrobiology Institute General Meeting, Washington, D.C., April
> 10-12, 2001 (in the latest issue of journal Astrobiology) that the
> Malin and Edgett gullies could represent "debris flows [from] large
> avalanches from thick dust deposits, analagous to climax snow
> avalanches." Treiman bases his model on the latitudinal distribution
> of the gully sites, which correlates to the large abundance of dust
> observed in the southern highlands, as well as to the dessicated
> nature of the Martian surface.

It seems highly reasonable that dry mass collapses would not show
the branching of channel piracy (which, if the flow were spreading
upwards, would not branch in that way for any obvious reason, and would
lead, instead, to a broader upslope collapse -- more alcove). Still, it
would be interesting to see simulations using martian parameters
instead of relying upon earth-condition analogues.


AND THEN
Alex wrote, quoting me:
--- In planetary_sciences@y..., "jarehling" <rehling@c...> wrote:

> You seem to suggest that the observed morphology of martian
> gullies is incompatible with dry mass movement...

Just to be clear, I am not referring soley to the
alcove-channel-apron morphology, which, especially for a wide array
of equatorward-facing examples, are attributed to dry mass movements.
However, with respect to the Malin and Edgett seepage sites, which
are observed finer scales, "the observed morpholog[ies]" (e.g.,
sinuosity, anastomosis, incision, streamlining, presence of levees,
channel/stream piracy, etc.) are indeed "incompatible with dry mass
movement."

For example, take a look at the dust avalanche scars reported by
Sullivan et al. and note the absence of these distinctive
characteristics. At any rate, it is not merely the observed
morphologies that suggest fluid flow, but also their spatial
distribution and preferential orientations.

> It seems highly reasonable that dry mass collapses would not
> show the branching of channel piracy...

Agreed.

[Guest_AlexBlackwell_*]

I'll repost the info in two installments in this post, each of which includes another post by quotation...

Ah, memories

[ljk4-1]

The Cornell professor who introduced Dr. Shinbrot to the
Martian gullies, Michel Louge, also studied the effects of
rocket blasts on the Martian regolith to see how far and
wide the rocket firings would kick the surface material.

He concluded that future rockets landing at Mars bases
may have to land far from the base to keep from "sand-
blasting" them. Louge felt that an airplane-like craft might
do better as a vehicle for a manned base.

http://www.news.cornell.edu/Chronicle/05/1...e_research.html

Any other studies on this subject? I have the feeling it is
one of those parameters of putting humans on Mars that
not many others have considered yet.

[Guest_paulanderson_*]

While the jury may still be out it seems on recent or current underground liquid water, there is a lot of subsurface ice apparently... see my posting here today with updated MARSIS news (LPSC, New Scientist, Sky & Telescope):

http://www.unmannedspaceflight.com/index.p...view=getnewpost

I still want a good explanation for the "seeps" as well, just as highly debated as the gullies...

[Guest_AlexBlackwell_*]

I still want a good explanation for the "seeps" as well, just as highly debated as the gullies...

I'm not sure the specific distinction you're drawing between "seeps" and "gullies." Just to be clear, though: when I use "seepage sites" and "gullies," I'm referring to the features discovered by Malin and Edgett, which they published in Science.

[Guest_BruceMoomaw_*]

Scanning through the LPSC Mars abstracts, the thing that struck me the hardest was that the Gully Wars are still on full-tilt. There are at least four totally different rival theories presented -- plus Allen Treiman's insistence, for the second year in a row, that the evidence points against ALL of them in at least some cases, raising the possibility that they're being made by different causes in different places.

Subsurface aquifers:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1666.pdf
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2049.pdf
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2412.pdf

Melting surface snow:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1610.pdf

AGAINST melting surface snow:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1201.pdf

Dust landslides:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1345.pdf

CO2 snow landslides:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1646.pdf

None Of The Above:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1304.pdf

But this, I think, is one mystery that will probably be settled by MRO, given its combination of very high-resolution surface photos, mapping of shallow subsurface aquifers, and extremely detailed near-IR mineral maps.

[Guest_paulanderson_*]

I'm not sure the specific distinction you're drawing between "seeps" and "gullies." Just to be clear, though: when I use "seepage sites" and "gullies," I'm referring to the features discovered by Malin and Edgett, which they published in Science.

Ok, by seeps, as nicknamed by some, I'm referring to the dark "stains" seen (from orbit) running down many crater walls or other cliff faces, distinct from the carved-out gullies. In case anyone here isn't familiar with these, some papers have suggested they are just what they seem to appear to be, short-lived episodes of water "leaking" onto the surface and then evaporating, leaving the "stains" which have been observed to then gradually fade / lighten over time, sometimes with "fresh" ones overlaying old ones. As usual, various papers have postulated various theories...

[Guest_Richard Trigaux_*]

It is sure that certain traces are dust flows, especially those dark traces that look so much like wet sand.

But ALL the gullies? I am not sure. There are meanders, and re-cut of the alluvion fan by further flows, which don't speak in favour of dust flows.

If you remember Burns Cliff panorama (by spirit before getting out of Endurance crater) there was such flow traces, which were very difficult to interpret: mud flows or dust flows?

Dust flows have the advantage to form into the actual martian climate. But they have some inconveniences: -Why we don't observe similar dust flows on the Moon (only landslides traces in recent craters like Tycho). -to be still active today, they need that martian grabens are still active (an explanation which don't hold when found in craters) or that there are intense Mars quakes.

Water flows require a recent period where Mars had more atmosphere, allowing for ice forming on certain slopes, and then melting to form the gullies. Why not? But if so the water of the gullies had to be released suddenly to make the flow traces (which imply a large flow rate). But after this high flow gets suddenly stopped, when there is no more slope, most of the time it don't continue as a river bed (although such river beds are observed too). This rather speaks for dust flows, or implies some special mechanism, for instance a snow cap keeps cool despites the sun, but it melts suddenly, pooring the water on a hot slope where it evaporates quickly, or is lost in sand.

So all this is not really clear and still deserves studies.