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Rover snapshots catch whirlwinds in action.

Movies of dust-filled whirlwinds on Mars have been sent back by NASA's exploration rover, Spirit.

The Mars Global Surveyor orbiting probe has seen these 'dust devils' before, but Spirit's close-ups reveal much more detail about the miniature tornados. "This is the best look we've ever got of the wind effects on the martian surface as they are happening," says Mark Lemmon, an atmospheric scientist from Texas A&M University, College Station, who is part of the rover team.

The robot is currently in the Columbia Hills overlooking Gusev Crater, the vast plain where it landed 463 days ago. Last month, the rover accidentally snapped a handful of blurry dust devils with its navigation camera. But the images showed little detail.

So the rover team told Spirit to take several series of 21 pictures, focusing on areas where dust devils were likely to be found. The pictures were taken about 20 seconds apart, on 15 and 18 April.

The dust devils are caused by convection currents set up by the temperature difference between the sun-baked surface of Gusev Crater and the chilly air above. Tracking the devils reveals which way the wind blows on Mars, and how they contribute to larger dust storms, helping scientists to build up a detailed picture of martian weather.

Spirit was actually hit by a dust devil in March, which helpfully swept clean its solar panels. Although dust build-up had reduced Spirit's power output by almost half, this spring-clean boosted the solar power back up to 93% of its original capacity.

The rover is now trundling over to a rocky outcrop nicknamed Methuselah, so called because the team believe it to be extremely old. They plan to study the rock in detail over the weekend.