Tag: dust devils

The inexplicable behavior of Martian dust devils

11:49 am

The inexpicable behavior of Martian dust devils
Click for original image.

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

1:12 pm

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!

11:44 am

Martian dust devil!
Click for full image.

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

3:42 pm

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
Click for full image.

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
Click for full image.

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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