DGerman-speaking meteorologists scientifically refer to them as “small trombones”, because of their often high dust content they are called “dust devils” in America, in Australia they are known as willy-willies: short-lived whirlwinds, typically a few meters in diameter, which – in contrast about tornadoes – form without the involvement of clouds. This often happens in desert areas, but you can also meet them here on dry summer days. Small vortices form when warm air begins to rise locally and starts to rotate. Then there is a drop in pressure inside them and increased wind speeds in the direction of rotation.
They have also been a well-known phenomenon on Mars since the first landing missions of the two American “Viking” probes in 1976 – and sometimes a welcome one. Because more than once have dust devils in particular the two solar powered Mars rovers Spirit (active on Mars from 2004 to 2011) and Opportunity (2004 to 2018) blew the red Martian dust off the solar cells. Now NASA researchers have published the recording of the sounds of a dust devil on Mars in “Nature Communications”. On September 27, 2021 it is directly above the rover operating on Mars since February 16, 2021 Perseverance swept away, which, as a nuclear-powered device, is not dependent on a cleaning service. The Supercam instrument’s microphone registered two gusts of wind about two seconds apart. In the windless interval between, the rover was in the eye of the vortex.
Images of the bugged dust devil taken with the Perseverance rover’s Navigation Camera (Navcam) in Jezero Crater on Mars. The images have been processed to reveal the amount of dust in the air. The dust color scale ranges from low (blue) to high (yellow).
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Image: NASA
The dust devil has also been observed with cameras (see picture) and tracked with instruments that register the impact of dust particles. From the data, the researchers conclude that this Martian trombone was 25 meters wide and at least 118 meters high. Their speed when they encountered the rover was about 5 meters per second.
The encounter with Perseverance was purely coincidental – the rover was not deliberately steered into the hurricane. However, earlier observations showed that dust devils form particularly often in its operational area – the 45-kilometre-wide Jezero crater on the edge of the Isidis Planitia lowlands, which was filled with water for a while during the Marsurian period. According to the authors of the now published study, the reason for this is still unclear.
By studying Martian dust devils, planetologists hope to gain better insights into how dust is stirred up and transported on Mars. By doing so, they hope to better understand Mars’ “dust cycle” and predict dust storms, particularly those that rage planet-wide every few years and then disrupt the various active Mars probes. Finally, dust is also an environmental phenomenon that afflicts the hardware humans send to Mars.