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borman
2009-Mar-21, 12:34 AM
On Recent Albedo Changes Observed In Martian Gullies

Over the past few years, there have been monitored by both the MOC and the HiRISE camera examples of recent brighter albedo streaks in gullies that have taken place over the interval of observation.

There have been speculations that the recent bright albedo contrasts might be due to new deposits and further whether the deposits were emplaced by dry or wet flows. The first reports were by Malin and Edgett from data from near the end of the MGS mission and later observations by the MRO team.

Malin and Edgett considered the possibility that the albedo contrast may have been caused by a wet outflow that brought brighter deposits to the surface and the MRO team has been considering a dry flow to source the postulated deposits. Meanwhile CRISM has detected no signal above background when looking at the postulated deposits.

A new paper will be given at the upcoming LPSC2009 conference that appears to question whether it is at all possible for a dry flow from above can source the entire postulated deposit over the length observed:

New Insights Into the Dynamics of Martian Gullies

http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1784.pdf

It might appear, superficially, that the paper does not support the MRO teamís interpretation of a dry flow to emplace a deposit of material that has a brighter albedo than background.

However, there can be a perspective that is consistent with both the present paperís authors study and the MROís authors dry flow hypothesis:

Rather than supposing that new material of a brighter albedo has been deposited, take the CRISM negative result as being significant and consider that the dust that covers these gullies as being darker than a brighter substrate. Then a brighter albedo contrast occurs if the darker dust flows down slope leaving a cleaner brighter contrast in its resulting absence on that portion of the slope that was covered before the event. If one carefully observes a bit down and left to the bright albedo streak, one can make out an enhanced streak that is darker than background. To make it more apparent, one can enhance the contrast on the IAS viewer to make the darker region stand out better. The distance that the dark flow subtends appears to be well within the constraints imposed by the LPSC 2009 paper and is still is consistent with the dry flow model supported by the MRO team without making a need for a water flow to support the dark deposit length.

Basically, the emphasis shifts from postulating new deposits that have a bright albedo to a cleaning event that removes darker albedo material further down slope.