‘butterfly’ Impact Crater In Hesperia Planum Options

[Rakhir]

‘Butterfly’ impact crater in Hesperia Planum

http://www.esa.int/SPECIALS/Mars_Express/SEMZLM8A9HE_0.html

[edstrick]

Mars has a 10x or so excess of oblique impact craters compared with the moon and mercury and ganymede/callisto. Back in the 80's, Pete Schultz noticed that they vary in orientation of the long axis of the craters, with the older, more degraded having a greater tilt relative to the equator than the younger ones. He proposed that the majority of them are the results of tidal decay of a pieces of one or more disrupted moons that were close to Mars than Phobos, and that their orientations reflect the equatorial plane of Mars *AT THE TIME* of the tidal decay and impacts. He argued (others have suggested, also) that the formation of the Tharsis bulge caused a shift in the moments of inertia of Mars, and caused true polar wander from some 4 billion years ago to the present, as Tharsis grew.

I don't think there were any really strong arguements against his hypothesis, but it was not generally accepted and there was little or no followup research by the early 90's on the idea. I don't know if there's been any more since.