[X] My Assistant

[fredk]

What's rising?
http://mars.jpl.nasa.gov/msl-raw-images/pr...NCAM00545M_.JPG

[fredk]

I didn't realize they could trigger from REMS. Very cool. It is hard to say how large it is. All we have to go on is that the entire visible slope of the central mound darkens in frame 2, including the little peak way off to the left. But the visible local horizon doesn't darken noticably. So the dust must be beyond the local horizon, which, given the extent of the darkening, suggests it is very large. Presumably from the timing and some estimate of wind speed we could get an estimate of the size.

Ed - I can't see any way this could be exposure variations. Between the first two frames, eg, the central mound darkens while the foreground stays about the same brightness. Exposure variations would brighten/darken everything uniformly, or maybe in some nonlinear way accounting for lut's and stretching. But whatever the details, all pixels with some particular pixel value must be mapped to the same pixel value after the exposure change (if the scene remains the same, of course). You shouldn't see some parts of the frame with some shade of grey mapped to different shades of grey than other parts with the same original shade of grey.

I'd add one more change to Ed's list. For the first two frames, the sky is brighter than in the other frames. This is all consistent with a gust passing over. The extra dust in the gust would brighten the sky as it passes over, while shading the ground.