Good to know that perseverance rover has touched the surface of Mars finally. We will have nice new opportunity window for exploring our closest "friendly" planet of solar system. Here's one of Mars photos perseverance has made :

enter image description here

Question is, What are this object roots marked with rose color ? I suspect it can be remains of past river in Mars or is it just an artifact of wind+sierra effect ?

  • $\begingroup$ They look like they are at the top of an escarpment, and so could be caused by material falling down the slope, crater rims often have such ridges at their edge, but this escarpment might be alluvial. $\endgroup$
    – James K
    Commented Feb 28, 2021 at 12:21
  • $\begingroup$ Yeah, I also think more about alluvial case, because it can be seen in picture that this sediments network is highly periodic (grate-like structure). This happens when some constant force (like water) is pushing forward various sediments on the floor. $\endgroup$ Commented Feb 28, 2021 at 12:47
  • $\begingroup$ But if my reading of the topography is right, this is at the top of a cliff, and water doesn't usually run along the top of an escarpment. $\endgroup$
    – James K
    Commented Feb 28, 2021 at 12:50
  • $\begingroup$ Hm.., I'm not the expert of topography. Can you please expand your knowledge in topography that this structure is really located at top of a cliff ? Btw, there are some cases of water running on top of cliffs,- see waterfalls. $\endgroup$ Commented Feb 28, 2021 at 12:55
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    $\begingroup$ I agree with @JamesK - This looks more like an escarpment than a river. However, what you didn't outline, to the right of what you did outline, might well be a former river. $\endgroup$ Commented Feb 28, 2021 at 17:06

1 Answer 1


The image in question appears to come down from the rover "down-look" camera. Here is a raw image of that, while this is a raw image taken next to it (you can line up the crater part in the left of the first with the main crater in the second).

While both list Sol 4 as the acquisition date, they list Feb. 23 and Feb. 24 as the Earth dates, while local time is separated by just 14–15 minutes. Despite those dates, which seem pretty incompatible to me, I have a feeling that that's when the images were downlinked to Earth from the rover. The "down-look" camera is "mounted beneath the rover, looking downward at the surface during landing." And, those do not look like images of the surface to me that I would expect if you were just a few inches away, instead they look like meter-scale pixels, not millimeter-scale pixels. So, I think these were images taken while it was landing, a few minutes apart.

Given that premise, I looked at a close-up of the HiRISE image of the landing site, which is nominally 25 cm/pix, and that crater in the second image matches the crater in the HiRISE image on the left, just rotated about 90° clockwise. So, this was a descent image, not an image from the surface.

With that knowledge, those are sand ripples, which are basically small dunes. These are all over Mars, so it's nothing unusual and does not have anything to do with it being near or in a lakebed, but just have to do with the wind and particle size of the martian regolith.

  • $\begingroup$ Thanks, I thought about this opportunity also, seems it's simplest explanation indeed. $\endgroup$ Commented Feb 28, 2021 at 20:23

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