[X] My Assistant

[dilo]

...and finally we have also some pseudo-color (L257) of the rover tracks after unstuck:

I'm intrigued by darker material in the left border of the trench, it appear also different in color ("less brown"); could be simply more recently excavated/collapsed terrain?
The left track image quality si poor but it seems to not exhibit this anomaly...

[Astrophil]

While we wait (hope) for colour pictures of that strange dark spot on the dune -

These images are cropped from navcam photos taken on the 18th -

1N172043947EFF55V4P1914L0M1
1N172043947EFF55V4P1914R0M1
1N172043999EFF55V4P1914R0M1

with brightness and contrast boosted, and then the application of the remove dust/scratches feature from Adobe Deluxe (best I've got, I'm afraid).

What they seem to me to suggest is that the spot might have a tail – on its downslope side, away from the dune crest, there are three little blots in a line. And the downslope border of the spot seems relatively straighter, whereas the upslope border is more semicircular. (There's a hint of these features in the more recent navcam images, if someone could enhance them better).

I wonder what the implications of this tail would be for the nature of the spot?

Attached thumbnail(s)

 

[dilo]

While we wait (hope) for colour pictures of that strange dark spot on the dune -
...

I have an hypothesys: could be the dark spot a "tiny crater" completely filled with fresh (darker) sand?

[dvandorn]

Hmmm... could be. But I doubt either the lighter drift material or the darker "stained" material are very fresh.

The stain might be the remnants of a rock or clod tossed out from a nearby impact, that made a crater in the drift a *long* time ago. The drift built up, covering the crater and the clod that produced it, and now the new prevailing winds are deflating that old drift and exposing its remnants.

Or perhaps a small impact produced a little crater in a light-colored drift, and that event was followed for a little while by a change in wind that deposited a darker dust. Now, the old drift is being deflated, the darker layer has been blown off of the remnant drift but the dark dust that once filled it is visible in what used to be the very bottom of a larger hole.

I *don't* believe it was a fairly recent crater that was filled in with dark dust, because if that had happened, we'd see more evidence of mantling of other features by this dark dust. And we really don't see any major layers of this shade of dust anywhere else that you could state with any certainty is a part of the same material as the "stain."

So much of the Martian surface is being deflated at larger scales, as is obvious from a lot of the orbital imagery, that it shouldn't be surprising to see surface deflation occurring at local levels, too.

-the other Doug