Looking at an image taken by Mars Odyssey THEMIS (Thermal Emission Imaging System) camera of an unnamed crater in Aonia Terra region I noticed what looks like grooves or ridges that resemble a stair like pathway, in what seems like perpendicular direction to water flow.

Here is the Aonia Terra Region of the image:

enter image description here

Here is the full image from THEMIS:

enter image description here

Finally, here is the closeup of the area I am talking about:

enter image description here

As you can see, on the top-left corner, there seems to be what looks like water outflows, which suggests to me that that corner of the region is "lower" than the other circled area in the lower center of the image.

Question is, what could create these ridges that look like stairs or a pathway?

  • $\begingroup$ Could it be Erosion Effects from Marsian winds? $\endgroup$ Jan 16, 2019 at 18:56
  • 1
    $\begingroup$ Looks like the Martians have moved beyond their canals and are now building railroads. $\endgroup$ Jan 16, 2019 at 18:57
  • 2
    $\begingroup$ difficult to say without a detailed elevation map of the area. $\endgroup$
    – Hobbes
    Jan 16, 2019 at 19:16
  • $\begingroup$ How would the elevation details will tell you anything about the surface formation? $\endgroup$ Jan 16, 2019 at 20:09
  • $\begingroup$ @Geordi La Forge - As per the answer by hdhondt and the whole face on mars thing working out heights from a single image is hard. Looking at something like radar altitude data for the area would give a much better idea of how much is conventional erosion. $\endgroup$ Jan 17, 2019 at 8:36

1 Answer 1


If I understand your question correctly, you are looking at an optical illusion. Depending on the direction of the light, craters can look like hills or vice versa.

If you flip your photo upside down, the ridges look like grooves, as you can see in this image:

enter image description here

  • $\begingroup$ Yes. I guess I should have used that wording. Grooves instead of ridges. What can cause grooves? $\endgroup$ Jan 17, 2019 at 16:01
  • $\begingroup$ After rotating, the grooves appear to flow downhill, as expected from water (or other) flow. But you really need elevation data to confirm this. $\endgroup$
    – hdhondt
    Jan 17, 2019 at 22:11
  • $\begingroup$ I am not sure we talking about the same features here. After rotating the image, the water flow is on the bottom right now. That clearly indicates that the rotated image has the lower bottom right of the image really lower than the rest of the topology above it. That ridges or groves still do not align with the water flow direction. $\endgroup$ Jan 18, 2019 at 16:00
  • $\begingroup$ How do you tell what the "water flow direction" is? I cannot find that information in your images. $\endgroup$
    – hdhondt
    Jan 19, 2019 at 0:10

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