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View Full Version : Damp-like Treadmark On Mars?



zenbudda
2012-Oct-05, 09:20 PM
From time to time (when I have time) I try to keep up with various things "related to astronomy". I came across this article/image from JPL:

http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1368

So, here's my limited knowledge of Mars:

1. Has very little atmosphere
2. Lower gravity than earth
3. Significantly colder than earth (and that's during the day)
4. Still questionable on whether H2O is present (however, it may be unlikely)

So, some of this could be wrong, but that's my general understanding (as amateur as it may be).

My question is this. Those treadmarks look EXACTLY like what I would expect on a wet sandy beach. I have also been in a VERY dry desert on a sand dune (both on foot and on a dune buggy). The tracks don't look anything like this since the sand is too dry. What conditions are causing this track to look like Curiosity drove over wet sand (wet from H2O or some other liquid)?

Swift
2012-Oct-05, 09:45 PM
I doubt it is moisture. I suspect it has everything to do with the microstructure of the powder.

I assume what you find "damp-like" is that it is such a sharp impression, and that the powder doesn't flow back into the treadmark. And yes, on Earth that could be caused by moisture, which can act to make the particles stick to each other, and not flow back into the treadmark.

But on a dry Earth sand dune, the particles are also most likely rounded, and thus would flow fairly easily.

I don't know what the nature of these particles are, but if they are not rounded, then rough, jagged particles can also stick together. IIRC, that is actually pretty common on the Moon.

I don't know that the particle roughness is the explanation here - I'm just saying there can be alternative explanations, particularly under non-Earth conditions.

glappkaeft
2012-Oct-05, 10:44 PM
The typical Earth example of this phenomena are imprints in compacted flour.

Ara Pacis
2012-Oct-06, 06:13 AM
Or corn starch, which is used to make somewhat detailed temporary/friable molds for casting gummi bears and worms and other treats, similar to how sand is used to make molds for cast iron.

kamaz
2012-Oct-06, 11:51 AM
Also, see footprints in silicate dust on the Moon...

zenbudda
2012-Oct-08, 03:34 PM
Thanks for the information. I did not realize that martian soil was a fine powder.

Swift
2012-Oct-08, 10:30 PM
Thanks for the information. I did not realize that martian soil was a fine powder.
Actually, I don't know how fine it is, and a coarse powder (bigger particles) might actually flow more poorly than a fine powder.