Scientists learning to predict dust devils on Mars


Posted: April 6, 2012

Knowing exactly when and where to look for dust devils on Mars is still a matter of luck, but scientists are making inroads in forecasting the red planet phenomena, leading to two astonishing images of Martian twisters released in the last month.

The HiRISE camera on NASA's Mars Reconnaissance Orbiter collected the imagery. NASA has released sharp color photos captured on Feb. 16 and March 14.

"This season is northern spring on Mars," said Richard Zurek, MRO's project scientist. "At this time, the ground is getting hot, and when the ground gets hot, it can produce dust devils."

Both images show dust devils in a region named Amazonis Planitia, a volcanic plain covered in dust. Amazonis Planitia is located west of Olympus Mons, the solar system's largest volcano, according to Zurek.

HiRISE is a telescopic three-color high-resolution camera providing the sharpest imagery of the Mars surface ever collected from orbit.

"We acquired some accidental dust devil images in previous years and found that we could measure rotational velocities from our three-color images," said Alfred McEwen, the HiRISE principal investigator at the University of Arizona. "This led to targeting dust devils for more measurements."

After discovering they can measure wind speeds inside the Martian twisters, researchers narrowed dust devil activity to the Amazonis Planitia region from low-resolution imagery.

"We've only been trying this for a few months and have only tried this a few times so far, but Mars is just starting northern summer, when we expect this area to be most active," said Colin Dundas, a researcher at the U.S. Geological Survey. "The early results look promising."

Despite clocking Mars dust devil winds of more than 65 mph, scientists say an astronaut on Mars would barely feel it. The red planet's atmosphere is much thinner than Earth, but dust grains carried by dust devils could scratch the visor of an astronaut's helmet, according to scientists.

HiRISE will continue searching for dust devils for further studies.

"HiRISE has a central color swath, and we construct color images by imaging through different color filters," Dundas told Spaceflight Now. "The color filters scan a given point on the surface at slightly different times, so if something like a cloud feature in a dust devil moves relative to the surface, we can see the movement and measure the velocity."

The winds measured in dust devils so far indicate the columns of the twisters may have a pressure differential of about 1 percent below the ambient atmosphere, enough to lift dust off the surface, according to a paper by Dundas and David Choi, a planetary scientist at NASA's Goddard Space Flight Center.

"We were only able to make measurements of four dust devils for that paper," Dundas said. "We've been trying to get more images so that we can expand on those results."

Photo and video credit: NASA/JPL-Caltech/University of Arizona

MRO's HiRISE instrument captured this image of a dust devil Feb. 16. The scene is a late-spring afternoon and the view covers an area about four-tenths of a mile (644 meters) across. North is toward the top. The length of the dusty whirlwind's shadow indicates the dust plume height. The plume is about 30 yards or meters in diameter.

A Martian dust devil roughly 12 miles (20 kilometers) high was captured winding its way along the Amazonis Planitia region of Northern Mars on March 14 by HiRISE. Despite its height, the plume is little more than three-quarters of a football field wide (70 yards, or 70 meters).

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