Click for full image.
Today’s cool image from Mars is cool both for what is visible in the photo and for what is not, the latter of which might turn out to be a discovery of importance.
The photo to the right, cropped and reduced to post here, was taken on June 24, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a section of the edge of Mars’ north polar ice cap, with north at the top.
This scarp is probably more than 2,000 feet high, though that height drops to the south as the upper layers disappear one by one from either long term erosion or sublimation. Those layers represent the visible information in the photo that is cool. They give us tantalizing clues about the geological and climatic history of Mars. Each layer probably represents a climate period when the north icecap was growing because the tilt of the planet’s rotation was even less than the 25 degrees it is now. When that tilt is small, as small as 11 degrees, the poles of Mars are very cold, and water ice migrates from the mid-latitudes to the poles, adding thickness to the icecaps. When the tilt grows, to as much as 55 degrees, the mid-latitudes are colder than the poles, and the water ice migrates back to the mid-latitudes.
What is not visible in this picture, however, might be far more significant.
The overview map to the right indicates this scarp’s location with the black cross, at the end of the canyon dubbed Chasma Boreale.
When this picture was taken it was springtime at the north pole. The Sun had finally peeked over the horizon, and begun warming the cliff face. In the past six or so Martian years, images from MRO have photographed hundreds of avalanches resulting from that warming, so many that the camera routinely captured events, as they happened.
Not this spring. In new images coming from MRO during the last few months there have been numerous icecap scarp photographs like today’s, taken of many different places, all designed to monitor the scarp for avalanches. Unlike past springs, however, in looking at these many images I have not been able to find any avalanches.
Obviously I could be missing them. I emailed Shane Byrne of the Lunar and Planetary Lab University of Arizona, who is involved in that monitoring, and asked him if my impression was wrong. It was not. As he wrote,
There have been fewer avalanches this year. To figure out how much fewer an analysis has to be done on how many kilometers of scarp were imaged in that season.
At the moment no one has completed that analysis, so no one knows exactly how much the count of avalanches has dropped, compared to past seasons. And if it has dropped, then that is a mystery that needs explanation. The change could simply be a random fluctuation, or it could be caused by some phenomenon that we as yet do not recognize. In order to gain a real understanding of Mars’ climate and seasonal changes this question needs answering..
The analysis required to do that however is likely not going to be done for awhile, There is so much new data arriving from Mars that there isn’t enough time to follow up every mystery, immediately As Bryne noted,
We’ll likely pick this up for the next extended mission proposal in an effort to explain why some years are different than others. Until then (next Spring) it might not get followed up on.
In other words, this mystery provides the MRO science team an additional reason to get NASA to extend the orbiter’s mission.
Of course, if some graduate student studying to become a planetary scientist needed a project now, I am sure their advisor would have no objections if they chose this one. Anyone interested?