9.08.2017

Martian dust devils: good for the climate, not so good for future space travellers

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The Red Planet is plagued by devils. It now seems that Mars’s surface is teeming with 10 times as many dust devils as we thought.

These rotating columns of dust form around low-pressure air pockets and are common on Mars, where they send dust into the atmosphere, controlling the planet’s climate. To get a better understanding of the Martian climate, as well as potential risks for future Mars missions, we need to know how many dust devils there are, but the barometers on landers there can’t detect all of them.

“They are only going to detect the biggest dust devils that have the strongest dips in pressure, and when they do detect them they’re going to give you a skewed image of the structure of those dust devils,” says Brian Jackson at Boise State University in Idaho. That’s because there’s no way to determine if they’re sensing pressure changes at the edges or in the middle of a whirlwind.

“Instead of telling us what was happening to the sensor, this work is telling us what was happening to the local Martian environment,” says Mark Lemmon at Texas A&M University in College Station.

Dust devils on Mars usually whirl across the surface for a few minutes before dissipating. And the team found that on any given day about one 13-metre-wide dust devil pops up per square kilometre of surface, on average. That’s about 10 times as many dust devils as originally thought, and they are also considerably smaller than earlier estimates that put them at 100 metres wide.

Mars’s surface area is almost 145 million square kilometres –  meaning that millions of dust devils blow across its surface every day. Jackson says if you were standing on the surface, you might be able to see dozens of kilometre-tall dust devils skittering across the ground at any one time.

“The place is really popping with atmospheric instabilities, especially in the afternoon,” when heat from the sun churns the atmosphere, says William Farrell at NASA’s Goddard Space Flight Center in Maryland.

Electric whirlwind

Dust devils are one of the most important ways that surface dust gets lofted into the atmosphere, where it traps warmth and is a crucial factor in controlling the planet’s climate and weather.

“Dust on Mars kind of fills the role of water on Earth: it’s the most important driver of weather,” says Lemmon. “Trying to understand how the dust gets into the atmosphere is key: you’re not going to get weather right if you don’t have that right.”

Understanding dust devils could also be important for our exploration of Mars. While the planet’s thin atmosphere keeps the high winds from being particularly dangerous since it’s not dense with gas particles like Earth’s, the dust grains themselves would be hard to keep out of spacesuits, future Mars shelters and just about everything else.

Plus, the static electricity from grains rubbing against one another in these dry, sandy whirlwinds could be a problem. “It’s possible that all of the dust grains clattering together in these storms could produce a lot of electricity and disable electronics,” says Jackson. “The electric fields associated with dust devils on Earth probably aren’t strong enough to be dangerous, but Mars is so much drier and dustier.”

Quelle: NewScientist