Orbiting camera measures swirling gusts in dust devils

By Nadia Drake

Web edition: October 14, 2011

Mars is not a placid place.

Among other things, dust devils carving trails through the planet’s reddish sands kick junk into its atmosphere. But though scientists have been able to estimate how quickly these devils travel across the rocky landscape, no one could really pinpoint the speed of the the swirling winds inside them until recently. Previous measurements of the extraterrestrial whirling dervishes’ interiors were rare, and fraught with complicated assumptions.

The devil is in the details, indeed.

Then along came David Choi, a postdoc at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Choi decided to track dust devil wind speeds using data from HiRISE, a camera on the Mars Reconnaissance Orbiter that snaps high-resolution photos of the planet’s surface. Sometimes, HiRISE captures a dust devil in action, creating a somewhat time-lapsed view of the devil’s progress. Using these lucky frames, Choi could track distinct cloud features within four individual devils and, knowing how much time had elapsed between photos, determine how fast the swirling clouds were moving.

The answer was somewhat surprising: In some cases, wind speeds within the columns whipped around at 45 meters each second — what we Earthlings would consider “hurricane-force,” or above 33 meters per second. Other times, the weather inside these alien tornadoes was milder, though typical wind speeds varied between 20 and 30 meters per second. He presented these results October 3 in Nantes, France, at the joint meeting of the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences.

“As a whole, they’re not like a hurricane, but there are pockets or gusts that exceed hurricane-force,” Choi says.

Some other funnies: All the devils were observed at roughly 3p.m. MLT. That’s Mars Local Time. They ranged from 30 meters to 250 meters in diameter, and towered between 150 meters and 700 meters into the Martian sky.