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Posted by: alan Oct 3 2005, 04:02 PM

Justin Shofler posted this image http://www.msss.com/mars_images/moc/2005/09/30/2005.09.30.S0800321.gif
on the other forum http://www.markcarey.com/mars/discuss-29672-plumes-from-venting.html
So what do you think? Are they deposits left by plumes or streaks caused by landslides?

Posted by: SigurRosFan Oct 3 2005, 04:07 PM

--- This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows outcrops of south polar layered terrain. Their appearance in this July 2005 springtime image is enhanced by bright patches of carbon dioxide frost. The frost is left over from the previous southern winter season; by summer, the frost would be gone. ---

http://www.msss.com/mars_images/moc/2005/09/30/

Posted by: 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.

Doug

Posted by: Richard Trigaux Oct 3 2005, 04:48 PM

mmmmmmhhhh....


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.

Posted by: babakm Oct 3 2005, 07:01 PM

This one is from the same region (203.51°W, 84.55°S) in 10-2003 with a bit higher resolution. No plumes. Don't think that it settles anything though as it's from a different time in the Martian year.

http://www.msss.com/moc_gallery/r10_r15/images/R10/R1004526.html

And this (203.61°W, 84.77°S):

http://www.msss.com/moc_gallery/r10_r15/images/R12/R1203465.html

Posted by: babakm Oct 3 2005, 07:10 PM

Hmmm. This one actually overlaps the image. Don't see any plumes, but I don't see any obvious rock formations that could be casting the shadows either.

http://www.msss.com/moc_gallery/r10_r15/images/R13/R1304106.html

Posted by: babakm Oct 3 2005, 07:59 PM

Excuse the triple post, but I've compared the negatives of the relevant portions of the images in the below attachment. Really looks like wind streaks to me.

Posted by: Richard Trigaux Oct 3 2005, 08:33 PM

interesting comparizon babakam.

We note that the "stakes" do not appear on the other photo: no trace of anything higher, or of its shadow.

But the wind streaks too do not appear. so they may be not permanent, or recent, or seasonal.

Very interesting. What could make dark streaks able to appear or disappear into some months or years? This implies the existence of a dark chemical, or a chemicals which decomposes into carbon. Methane?

A possible explanation would be a process of concentrating dust in some points when the ice sublimates ( a process common on Earth when dirty snow sublimates). But when everything is dry and cold, the wind could blow these dust pockets. The next seasonal cycle makes these dust streaks concentrate again into small pockets, and this become "invisible" from far. Such a cycle would explain many strange features in the polar ice caps: dark spots appearing with season, dendritic structures, etc.

The dust would be that ordinary martian dust, which would appear black on these photos where exposition was set short, in order to show features on the very clear ice.