Suffering from wind
Sarah Barnett goes in search of dust storms that make the ones pictured in the latest issue of Flipside, mighty as they are, look like gentle breezes…
Dust storms originate in the deserts of Earth, so what do you think happens when virtually the whole planet is a desert? The storms on Mars make ours look rather piffling, as you might expect.
Scientists first had their suspicions confirmed of Mars’ spectacular storms when Mariner 9 was orbiting the planet back in 1971. The probe found a Martian atmosphere full of dust that obscured the view of the surface. Mariner 9 stayed in orbit until the dust began to settle and it could begin its job of studying the surface details.
More minor dust storms happen all the time on Mars but, in 2001, there was a storm so big that amateur astronomers using modest telescopes could see it from Earth. Although Nasa’s Mars Global Surveyor, in orbit at the time, got the best view and measured the daily temperature and dust content of the Martian atmosphere.
The storm began as a small dust cloud inside the Hellas Basin, a 9-km deep impact crater in Mars' southern hemisphere. This then spilled out of the Basin and wrapped itself around the entire planet in a matter of weeks. It didn’t dissipate for about three months.
So how did this happen? The sun’s heat warms the Martian atmosphere and causes the air to move, lifting dust off the ground. As to how Martian dust storms grow to such proportions, one theory is that once airborne, dust particles absorb sunlight and warm the Martian atmosphere in their vicinity further. Warm pockets of air rush towards colder regions and generate winds. Strong winds lift even more dust off the ground, which further heats the atmosphere, quickly spreading round the planet.
Earth can’t produce such huge phenomena because of the large presence of water, whereas Mars’ dry, thin atmosphere helps raise winds and even more dust.
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