Click for full image.
Cool image time! The photo to the right, cropped and reduced to post here, was taken on January 29, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the science team labels as “Fresh Shallow Valleys”. The section I have focused on shows a particularly interesting meander next to a small crater. The full image shows additional similar channels to the north, with one draining into a larger 3.7 mile wide crater.
The location is in the southern cratered highlands, at about 41 degrees south latitude, where much evidence of buried glacial features are found. That certainly is what we appear to see here. In fact, the wider view afforded by MRO’s context camera reveals many more such channels. That wider view also shows a much larger 18-mile-wide crater just to the north that appears filled with buried ice.
That the scientists label these fresh suggests they think they are relatively young, probably dating from when the most recent cycle of glacial growth probably ended. This would make them about 6 million years ago, based on this paper [pdf] and the second figure from that paper below.
According this graph, it appears Mars’ rotational tilt shifted from about 40 degrees to its present 25 degrees today about six million years ago. When it was 40 degrees the mid-latitudes would have been colder than the poles, and thus water would sublimate from the polar icecaps to fall as snow in the mid-latitudes. Glaciers would form there and grow, flowing down to carve channels such as these.
Since then those glaciers have been inactive. Scientists think (though this remains uncertain) that the poles and mid-latitude glaciers are presently in a steady-state, with neither growing nor shrinking.
Thus, any glaciers in these channels are likely stable at this time. No additional snow is falling on their upstream ends to the west, so they are under no pressure to flow eastward downhill.
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