Click for full image.
Cool image time! The photo to the right, cropped and reduced to post here, was taken on August 7, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the many layered scarp that forms the edge of the northern polar ice cap on Mars, probably more than 2,000 feet high.
Those layers are significant, as they indicate the many climate cycles that scientists think Mars has undergone over the eons as the red planet’s rotational tilt, or obliquity, rocked back and forth from 11 degrees inclination to as much as 60 degrees. At the extremes, the ice cap was either growing or shrinking, while today (at 25 degrees inclination) it appears to be in a steady state.
Why the layers alternate light and dark is not known. The shift from lighter colors at the top half and the dark bottom half marks the separation between the top water ice cap and what scientists label the basal unit. It also marks some major change in Mars’ climate and geology that occurred about 4.5 million years ago.
The yellow cross on the overview map to the right indicates the location of this scarp. Because the pole’s scarps near the bottom of this map, where this photo was taken, tend to be less steep, most of the seasonal avalanches that occur in the spring are found along the scarps near the top of the map.
The origin of the hollow, where the scarp is retreating faster, is also unknown. For some reason something caused more erosion at this point. If it was an avalanche in the far past, all evidence of that event is gone. That the basal unit shows no such erosion suggests the origin is much more complicated than an avalanche.
One not obvious detail about this part of Mars is its daily weather. Though this is springtime and the Sun is out, it is very cold here, far colder than the coldest places on Earth. Though temperatures can get above freezing in the equatorial regions, at the poles that almost never happens. The planet’s average temperature globally is -81 degrees Fahrenheit. This means that at this spot the temperature when this photo was taken was likely well below zero degrees Fahrenheit, probably by many tens of degrees.
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