* Astronomy

Airbursts trigger dust avalanches on Mars

The surface of Mars may be cold and desolate, but it is not unchanging. New images show that avalanches of dust scour dozens of Martian sites each year.
Without the abundant water and plate tectonics that keep Earth's surface in motion, the surface of Mars is much slower to change. But in one way it is more active. While Earth's atmosphere shields us from asteroids smaller than 30 metres across, which burn up or shatter too high above the ground to have much effect on us, Mars's atmosphere is just 1 per cent the density of Earth's. Even rocks less than a metre across make it to the ground and gouge out craters.
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