QUOTE (djellison @ Oct 3 2005, 04:14 PM)
What confuses me is that it says Illumination, Upper Left.
MOC imagery is almost always illuminated from the left - as the local time is about 2pm when MGS goes overhead and thus, with north at the top - the sun is to the left - granted, that goes out the window when you're right down by the poles - but still, it SAYS upper left...
However - it really does look like something tall, illuminated from lower right.
They say the relief is outlined by patches of carbon dioxid frost. So from the beginning it is misleading: the clear side may be the shadowy side. And we do not have the usual craters to indicate us where the sun comes from...
This image makes sense if we assume lighting from upper left: the black streaks in the bottom (or gray in the middle) are wind deposits. Strange anyway, as it suggests there is a sort of venting sending some black dust. Venting what? perhaps carbon dioxid, gone since long ago, but which left these streaks.
But if we assume that lighting is from the bottom right, he vision of the relief is consistent too. It strongly suggests some high stakes.
My idea is that, even if we suppose a mistake, or a lie, about the lighting orientation, and that the lighting is really from bottom right, there are still some slight indices that tell us it is not so:
-the streaks are not all exactly with the same angle, as shadows would be.
-some streaks start from nothing visible. If it was a stake, tower or what else, it should be at least as large as the streak.
So I think these are really vents.
By the way this image is likely to be, not of layered terrains, but of the polar cap ice shield. There are often very puzzling things in there regions, such as black spots evolving with season, dendritic structures and so. So why not vents of some nature. Remember than on Earth the ice shields nearby alway lay on a thin layer of water, due to geothermal heating. As a result, there are springs in the front of glaciers. Is there the equivalent on Mars? In this case, the result is likely to be a gas flow at the top, as liquid carbon dioxid is lighter than its ice, and it cannot remain liquid near the surface.