[X] My Assistant

[Guest_AlexBlackwell_*]

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

[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.