A piece of Mars: What are those dark, flat circles and why are there little dunes sitting on top of them? They’re probably old impact craters that got filled in with dark sediment, and were then eroded flat. So you’re seeing the old crater floors — the crater rim and ejecta have all been eroded away. Dunes have formed out of some of the dark sediment that’s slowly eroding away. (HiRISE ESP_029422_2055 NASA/JPL/University of Arizona)

Comments (13)

  1. Lava Lakes … Mars was not a nice place to be back then …. mind you earth wasn’t either a little latter on, we are just going through our carboniferous phase. Do not worry Earth will look the same in a couple of billion years when the sun expands a bit. By then we will have sent our DNA spawn out into the cosmos on the next great journey. Perhaps 10% of mankind understand this, and are at peace.

    1. I doubt Mars was ever (on average) as warm as Earth, being farther from the Sun than Earth.

  2. I don’t if I agree with his statement. Bottom almost center Impact craters of the same size one over lapping the other with an edge as high as the other! doesn’t sound right. Looks more like bore holes made with a hammer drill. Possible core samples.

    1. They probably eroded a little differently, so different amounts of the crater floor are left standing. At ~20-30 meters across those would be quite impressive core samples.

  3. Thanks Lori. Posted on our FB/G+/Twitter. I wonder if you read/receive comments, so this is a test

    1. Yep/Yep. -Lori

  4. size of scale please.

    1. The scene is 300 m across (left to right). The small dark circle in the upper middle is ~24 m across.

      1. Thanks! Is the blue tint/hue due to artificial photo effect? looks like a surreal landscape, wish we can go there.

      2. Yep, it’s not really blue. The whole thing should be shifted more yellowish-red, so that it would range from a rust color to dark grays. I’m just stretching out the whole color range so we see more detail. I agree, Mars is pretty trippy! I want to go too. I wish I could do fieldwork there.

  5. a crater with wind swept sand dunes

  6. Could also be volcanic in origin? Might be more likely than an impact crater? Would seem to fit with the color schema, IMO.

    1. They’re unlikely to be volcanic. They’re located in an actively eroding area filled with many sedimentary layers, but no evidence of volcanism. This is in Mawrth Vallis, one of the final four candidates for Curiosity’s landing site (Gale crater won that contest, but the 2020 Mars lander may wind up here). Circles like these are found in many locations on Mars, always in layered terrain that is considered sedimentary. Impact cratering is one of the many geological processes that has shaped the landscape on Mars, along with sedimentary deposition and erosion. So it’s most likely these circles are old crater floors.

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