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[john_s]

Compare the treads between the earlier shot and this one.  Or even the top track's treads and the bottom track.  They are filling in and eroding away.

This, too me, is evidence that the dunes are currently active.  So it is not a matter of how old are the dunes, but how fast are they changing.

That's impressive- thanks for pointing out the changes. I'm not sure this is evidence for active dunes, though. The tops of the dunes are armored by a layer of blueberries and/or other coarse debris. Oppy's wheels have disturbed that armor, exposing fine dust which is then easily picked up and moved by the wind. The dunes themselves may not move unless the wind is strong enough to disturb the armor or somehow pick up grains from beneath it.

[dilo]

Mossbauer intrument made some pressure inside the right track (Sol 507) :

[RNeuhaus]

Mossbauer intrument made some pressure inside the right track (Sol 507)  :

Incredible fine sand like a powder. It looks that the sand has somewhat humidity because of the presence of cracks. Who else can tell more about this?

Rodolfo

[dvandorn]

A fine enough powder acts like this in the complete absence of moisture -- in fact, moisture keeps a fine powder from acting this way. Try pressing some flour down onto a plate and see what it looks like... you'll get cracks like this.

-the other Doug

[Jeff7]

A fine enough powder acts like this in the complete absence of moisture -- in fact, moisture keeps a fine powder from acting this way.  Try pressing some flour down onto a plate and see what it looks like... you'll get cracks like this.

-the other Doug

Thing is though, a dry day on Earth would probably be outright dank and humid for Mars. This is low grav, low air pressure powder here.

[dvandorn]

Yes, but an average day on Mars would be considered tremendously dank and humid (and air-filled) on the Moon, and you see lunar dust forming cracks like this, too. In the complete absence of air and water.

It has to do with the grain size and morphology -- fine powders become somewhat self-cohesive, especially in a vacuum or under low pressure. That's what causes the cracking action. As I said, it even works in our own atmosphere with most fine powders.

-the other Doug

[RNeuhaus]

Yes, but an average day on Mars would be considered tremendously dank and humid (and air-filled) on the Moon, and you see lunar dust forming cracks like this, too.  In the complete absence of air and water.

It has to do with the grain size and morphology -- fine powders become somewhat self-cohesive, especially in a vacuum or under low pressure.  That's what causes the cracking action.  As I said, it even works in our own atmosphere with most fine powders.

-the other Doug

I agree with you since I have ever observed the powder behavior. The powder has somewhat static attraction property that unites among powders.

Rodolfo