Click for full image.

Cool image time! The photo to the right, cropped and reduced to post here, was a featured image today from the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The caption, written by Carol Weitz of the Planetary Science Institute in Arizona, focused on the wind patterns created within these craters.

These impact craters in the northern middle latitudes have interesting interiors: all of them have wind-blown (aeolian) ripples.

Outside of the craters and along the crater floors, the ripples are all oriented in the same direction. However, along the walls of some of the larger craters, the ripples are situated radially away from the center, indicating the winds moving inside the larger craters can be influenced by the topography of the crater wall.

Additionally, many of the larger craters have layered mesas along their floors that are likely sedimentary deposits laid down after the craters formed but prior to the development of the aeolian ripples.

I am further intrigued by the rimless nature of these craters, as well as the lack of significant rocky debris at their edges. They all look like the bolides that created them impacted into a relatively soft surface that, rather than break up into rocks and boulders, melted, flowed, and then quickly refroze into these depressions.

The location, as always, provides us a possible explanation.

The white cross indicates the location of these craters, in an area just north of the region of chaos terrain dubbed Nilosyrtis Mensae, the easternmost part of that 2,000 mile long mid-latitude strip of chaos I dub glacier country because every image taken of the landscape there seems to exhibit glacial features.

Thus, it is very likely that there is a lot of ice very close to the surface at this location. In fact, that ice layer could be dominant, and its presence could easily explain the nature of these craters.

Obviously, that can’t be the whole story. We don’t know how long ago these impacts occurred, and in the interim erosion processes could have reshaped things by quite a lot. Moreover, the data is still somewhat sparse.

Below is a global map of Mars, indicating where scientists have found a lot of evidence of ice. The two lines at 30 degrees latitude indicate the range of detected persistent ice, near the surface. The equatorial regions have so far been found to be dry, though underground ice might still exist.

The regions outlined in white are those where extensive glacial and ice features have been detected as well. For the full resolution version click on the map.