"Two whirling dust devils towering nearly a kilometre high have been seen at the exact spot where the Phoenix Mars lander is due to touch down in a few weeks. The dust vortices should pose no threat to the landing, but could provide dramatic views from the probe when it alights on the flat, relatively barren landscape.
Phoenix is due to land in an oval-shaped region dubbed "Green Valley" in Mars's northern polar region on 25 May. In preparation for the landing, other spacecraft already at Mars, including NASA's Mars Reconnaissance Orbiter (MRO), have been monitoring the site.
On 20 April, MRO spotted two dust devils at the centre of the landing ellipse, which measures 20 by 100 kilometres across. Based on the shadows the dust devils cast on the surface, researchers estimate that one stretched to about 920 metres in height, while the other reached 790 metres.
Dust devils are created when vortices of air - set in motion when warm air rises from the surface on an otherwise still day - pick up dust from the ground. The dust reaches such great heights because of the Red Planet's relatively low gravity."
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