Click for full image.
Cool image time! The photo to the right, cropped and reduced to post here, was taken on February 2, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and shows a mesa sticking up on the relatively flat and featureless northern lowland plains in Utopia Planitia, the second largest impact basin on Mars.
The full image shows three such mesas. Though pictures taken in the northern lowlands of Utopia tend to show evidence of buried ice or glaciers, the impression I get from this picture is one of dryness. If there is any ice here, it is below ground. And even that seems unlikely. The surface surrounding nearby craters does not have that squishy and slushy look that is seen in the north when an impact occurred on near surface ice. Instead, the ground looks solid.
The overview map below reinforces this impression.
The red dot on the 30th parallel north of Isidis Basin marks the location of this mesa. At that latitude the mesa is at the very southern edge of the 30-60 degree mid-latitude bands where scientists have found many Martian glaciers. While a few spots south of that latitude have been identified where there might be ice, they are few and also uncertain. The general trend is dryness once one gets to 30 degrees.
These mesas are intriguing because they suggest that the surface here was once higher, and that a significant amount of material has been removed over the eons, with these mesas somehow surviving. This hypothesis is strengthened by what look like two pedestal craters just to the east of the mesa. Pedestal craters are thought to be impact spots that resist erosion because the impact smashes the material at the site and makes it more resistant to erosion. When the surrounding terrain erodes away, the crater remains.
What swept those top layers away? A first guess is that once there was underground ice here, and with its slow loss over time the surface dropped away.
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Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space
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