May 27, 2012

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Droppings From a Passing Mountain?

LRO WAC mosaic processed by Maurice Collins, New Zealand

While working on a secret project I came across this great LRO mosaic on Maurice's website. It was made a year or so ago, before the appearance of the LRO QuickMap. The image made me wonder if the large crater just beyond the chain's eastern end - Davy G - was related to the chain. The reason for thinking it might be is that G is elongated exactly in line with the direction of the chain. The QuickMap view (left) has a higher Sun angle showing G to be teardrop-shaped. Bill Ambrose has studied similar features called asymmetrical secondaries, finding that the small end points away from the source. If that is the case for this much smaller teardrop crater than it may have come from the west, perhaps being formed by a small mountain of ejecta, and the smaller craters in the Davy chain formed by materials that dropped off of the mountain as it flew eastward. This sounds pretty preposterous but I would expect that ejecta masses would be pulverized and that pieces would drop off as the ejecta flew by. The Davy Chain points back toward the Humorum Basin - which is too old to be the source of such a young chain. It has been argued previously that the Davy Chain might have resulted from Shoemaker-Levy type impacts of a gravitationally sheared comet of asteroid. An argument could be made that such shearing resulted in a series of small projectiles and one large one. But is it a reasonable argument?

Chuck Wood

Related Links
Rükl plate 43

Yesterday's LPOD: A Dome On the Limb

Tomorrow's LPOD: Anorthosite Rays


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