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Unmanned Spaceflight.com _ Mars Global Surveyor _ Then and Now

Posted by: MizarKey Apr 15 2006, 08:24 AM

Of course we've seen similar side by side images showing the changes between the years. I never get tired of them...

Here's a couple...from http://www.msss.com/moc_gallery/m13_m18/images/M16/M1600291.html 12.02m/pixel and http://www.msss.com/moc_gallery/s05_s10/images/S09/S0901626.html 3.21m/pixel

I rotated M1600291 so it would line up with S0901626. I didn't really scale them efficiently, M1600291 appears at 2x while S0901626 appears at 0.5x

You can see that a couple of the 'seeps' (dust slides or whatever) are new. The other section I enlarge 2x from S0901626 I thought interesting as the 'dust' passed over two outcroppings but only made them slightly darker while the rest of the trail is quite a bit darker...I would think the darkness would be more uniform...maybe the dust didn't stick to the outcrop so much?

Posted by: Phil Stooke Apr 15 2006, 11:45 PM

The moving dust isn't dark. It's the material underneath the bright surface layer of dust that is dark. The streak is a place where the bright dust has been disturbed.

Phil

Posted by: MizarKey Apr 21 2006, 04:31 PM

Is wind the proposed mechanism for the disturbance? Or some kind of dust avalanche that mimicks fluid movement?
I know it's considered 'looney' to think this may be some liquid based phenomenon, but based on the current level of evidence detail available, a flowing liquid (dirty brine, slush or whatever) fits the observations too. These trails are distinctly different than what we see in the dust devil trails, though I've yet to see a dust devil trail and one of these within the same crater or hillside.
My point being that I don't think anyone can authoritatively state that what we're observing is precisely one thing or another (action of dust or liquid). Of course I'm not as well read as some of the members here, so if there are scientifically authored papers on this I'd love to read them.
And please note I did not mention the H2O word once.

Posted by: ljk4-1 Apr 21 2006, 05:00 PM

Dr. Troy Shinbrot has examined granular flows where the tiny surface
particles of Mars in its lower gravity can and do act like a liquid.

See his paper here:

http://www.pnas.org/cgi/content/abstract/101/23/8542

Posted by: MizarKey Apr 22 2006, 02:43 AM

Thank you for the article. I like that they concluded by leaving the possibility open that their interpretation is not the only interpretation. It also doesn't look as if they were studying the dark stain-like phenomena seen in the image above, but more of the gullies and landslides. Still, it was a well done article.

Posted by: Richard Trigaux Apr 22 2006, 07:14 AM

I think the right image is too blured (compared to the left image) so that it is difficult to get any conclusion about a change. But you are right, MizarKey, we must stay alert as such changes are likely.

In some images, the dark stains strongly suggest they are made of some moisture flowing freely on the surface, and they raised much discutions on "another" cooks forum. But such an explanation is very unlikely, the explanation of dust flows is much better. But to hold, such an explanation requires that the slope is very smooth, also made of fine particules, like a dune equilibrium slope. A slope made of stones would not allow so easily for dust flow.

Posted by: MizarKey Apr 23 2006, 07:13 AM

There is nearly a 4:1 resolution difference between the older (right) and newer image. However, on the newer image there is a 'new' black streak about midway down the image on the left side. Not much of a change in 5 years, but at least something is happening on Mars and it's not just a static place.

Posted by: Richard Trigaux Apr 23 2006, 07:29 AM

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Yes I found it, a thin one but very dark (more fresh than the others). It is a bit confusing, we could confuse with other smaller tracks, but this one seems new, and we can rely on the shape of the nearby rocks to compare and eliminate confusion with the other smaller tracks. I am not certain, but you are anyway right that we must stay alert. That only some things like that are found, and it would give us a clue on how common they are in time.

What we don't know is how fast such avalanches flow? is it a creeping process, which could take thousands years, or a catastrophing process lasting some seconds? The only thing sure is that this time is much shorter than the time needed to whiten the traces (otherwise we should see tracks with the top white and the bottom dark). And I guess it is not fast enough to have inertia effects on the avalanches.

We don't know too how many time is needed to whiten the tracks. After what we saw on Spirit and Oppy's solar cells, dust can be deposited very fast, and a change in colour could come in only some years. Then the time between two avalanches in the same place would be in the thousands years, at rough guess. And tens of such avalanches could take place every year on Mars. The odd for an amateur to spot one is still low, as only few images are available on the net for comparizon. Perhaps a software could work on images to find such changes.

Posted by: MizarKey Apr 24 2006, 07:03 AM

Richard, I don't know if you've seen the site http://www.marsunearthed.com/Contents/Contents.htm. They've done some very nice work on comparing MGS images of the same areas. Check the last two links on the page I linked above.

Posted by: ljk4-1 May 31 2006, 06:08 PM

Some interesting gullies from MGS:

Breaking Trail (Released 25 May 2006)

http://www.msss.com/mars_images/moc/2006/05/25