The global distribution of dust devils on Mars

Global map of dust devils on Mars
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Scientists reviewing the dust devil tracks in orbital images produced by Mars Reconnaissance Orbiter (MRO) have now created a global map that also provides insight into the ground conditions that cause the dust devils to form. From the abstract:

In the first global study of these tracks using high-resolution satellite images from 2014 to 2018, we find tracks in 4% of the images, mostly near 60° north and south latitudes. These tracks are more common during local summers, especially in the southern hemisphere, coinciding with the peak of Mars’ dust storm season, when active dust devils are also more common. Surprisingly, dust devil track (DDT) formation does not depend on elevation, indicating it is not related to the ambient atmospheric pressure. Instead, they occur in darker areas where surface dust covers coarser material, which is revealed as the dust devil moves past.

The white dots on the map above, figure 5 of the paper, shows those MRO images where dust devil tracks were seen. The redish-orange regions are where the data suggests more dust devils should occur, while the blue areas of regions of few dust devils.

The map also notes the locations where Spirit, Opportunity, and InSight landed. Opportunity clearly landed in a region that had more dust devil activity, which explains why its solar panels were cleaned off so regularly by wind. Spirit did not land in such a region, but somehow it was lucky in getting wind events that cleared its panels of dust. InSight had no such luck, and having landed in a region with little dust devil activity, its panels steadily became covered with dust, eventually forcing the end of the mission.

As the paper notes, “To maximize mission lifetimes, future solar powered assets should favor regions where we have identified numerous [dust devil tracks] and where many active [dust devils] are present.” This proposal makes sense, for many reasons. For one, it shifts missions to higher latitudes where many glacial and near-surface ice features are found. Up until now the science community has sent all the landers and rovers to the Martian dry tropics, which has no such near surface ice. For future colonies it is imperative we begin studying Mars’ wetter regions.

This study provides another practical reason for doing so.

Monitoring a changing spot on Mars

Monitoring a changing landscape on Mars
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on July 18, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Based on its label, “Dark Filamentary Streak Year-Round Monitor Site in Promethei Terra,” it was apparently taken as part of a long-term project to monitor the changes that occur at this particular spot on Mars.

This monitoring began in 2008, not long after MRO began science operations. In that first image, taken in the Martian autumn, almost the entire terrain was covered with dust devil tracks, all running more-or-less parallel to each other in a northwest-to-southeast direction.

That unusual tiger-striped landscape prompted later monitoring. However, a follow-up photo in 2010, also in autumn, showed practically no dust tracks here at all. Another image, taken in 2011 during the Martian summer, showed new dust devil tracks, but instead of being aligned as in 2008, the tracks went in all directions, with only a hint of alignment to the southeast.
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The inexplicable behavior of Martian dust devils

The inexpicable behavior of Martian dust devils
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Today’s cool image illustrates the puzzling inclination of Martian dust devils to strongly favor specific regions on the Martian surface, for reasons that at present no one can confidently explain.

The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 28, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a plethora of dust devil tracks, almost all of which have an east-west orientation. Moreover, the tracks seem uninfluenced by the surface topography, continuing on their path without deviation, even as they cross cliffs, craters, and mounds. The orientation tells us the direction of the prevailing winds, though I don’t know if those winds blow to the east or to the west.

What makes this image revealing is that a gathering of such dust devil tracks is seen so rarely in other MRO high resolution photographs. I look at a lot of MRO pictures, and though dust devil tracks are not rare, most images don’t show this many. Apparently, there are specific conditions on Mars that cause a lot of tracks to appear in specific locations, either because atmospheric conditions create a lot more dust devils, or the ground conditions allow the tracks to become more visible.
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Changing Mars

The maculae splotch dubbed Maui
For the full images click here (2019) and here (2020).

While Mars appears to be a dead planet, with no clear evidence of life so far discovered, the planet is hardly inactive. Things are changing there continuously, even if it happens at a slower pace than here on Earth.

To the right are two images, rotated, cropped, and reduced to post here, taken by the high resolution camera of Mars Reconnaissance Orbiter. The first was on January 19, 2019, shortly after the end of the global dust storm that engulfed Mars during that Martian year. The second was taken on February 14, 2020, half a Martian year later. Both show one of a string of dark splotches located on the western flanks of the giant volcano Olympus Mons. Scientists call these splotches maculae, and because of their superficial resemblance to the islands of Hawaii, have given them names matching those islands. This particular patch is dubbed Maui. Below is a map showing all the splotches and their position relative to Olympus Mons, taken from a 2019 presentation [pdf].
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Martian dust devil!

Martian dust devil!
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Cool image time! The science team for the high resolution camera today posted a new captioned image, cropped by me to the right to post here, showing an active Martian dust devil as it moves across the surface of Mars.

Dust devils are rotating columns of dust that form around low-pressure air pockets, and are common on both Earth and Mars. This Martian dust devil formed on the dust-covered, volcanic plains of Amazonis Planitia. The dust devil is bright, and its core is roughly 50 meters across. The dark streak on the ground behind the dust devil is its shadow. The length of the shadow suggests the plume of rotating dust rises about 650 meters into the atmosphere!

That’s about 2,100 feet tall, almost a half mile in height. The location, Amazonis Planitia, is part of the northern lowlands of Mars, flat and somewhat featureless. It is also somewhat near the region near Erebus Montes that is the candidate landing site for SpaceX’s Starship rocket, a region that appears to have a lot of ice just below the surface.

The science team also linked to a 2012 active dust devil image that was even more spectacular. I have also posted on Behind the Black a number of other dust devil images, highlighting this very active, dramatic, and somewhat mysterious aspect of the Martian surface:
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A dance of dust devils

A dance of dust devils on Mars

Many of my image posts about Mars have emphasized how slowly things change there. This post will highlight the exact opposite. When it comes to dust devils, it appears they can leave their trace frequently and often, and for some reason they seem to also favor specific locations.

June 2011
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The string of images above are all of the same location in the southern highlands of Mars. All were taken by the high resolution camera of Mars Reconnaissance Orbiter (MRO) and can be found in the camera’s archive. I have cropped them to show the same approximate matching area. The first image in that strip above, shown at higher resolution to the right, was taken in June 2011 and titled “Possible Gully Features” by the MRO science team. This is not surprising, as the rounded hills in this image are actually the southwest rim of a large crater, and the slopes of craters have been found one of the best places to find the gullies where seasonal changes occur, all possibly caused by underground water.

From the title, it appears that the science team might have first hoped to spot either slope streaks or recurring slope lineae, the two most intriguing of these changing features. Instead, that 2011 image showed them a very eroded crater rim with a small scattering of dust devil tracks.

November 2018
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This lack of gullies probably reduced interest in this location. It wasn’t until seven years later, in November 2018, that the MRO team decided to take another image of this location (the second image in the strip above and shown to the right at higher resolution). This time they found a significant increase in the number of dust devil tracks.

At this point the decision must have been made to take another image of this location a month later in December 2018. I assume the scientists were curious to see if they would spot any additional changes in that one month period. This was dust devil season, so the likelihood of seeing more tracks was not unreasonable.

How many tracks appeared, and whether they were concentrated in any particular place, such as the ridge lines, would help researchers better understand what generates them, which in turn will give them a better understanding of the Martian atmosphere.

The result was astonishing.
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