Chasing Dust Devils from Earth to Mars

Matt Balme thought of a tornado when he saw his first dust devil near Phoenix, Arizona. Now he looks forward to spending next summer chasing down dust devils in a four-wheel-drive truck to help understand how such phenomena shape the Martian climate.

Scientists suspect that dust devils on Mars help lift dust into the atmosphere and may feed the planet's giant dust storms, but they have yet to directly measure a dust devil on the red planet beyond some pressure readings and a few fleeting images.

Terrestrial dust devils are seen as a decent analogue for their Martian cousins.

"We're really hoping to be able to provide raw data, hard numbers for people doing models for the Martian climate," said Balme, a planetary scientist who splits his time between the Planetary Science Institute in Tucson, Arizona and Open University in the U.K.

Local twist

The hair-raising research aims to gauge the number and intensity of Earth dust devils within a one-square kilometer area bounded by three meteorological stations that will measure wind speed and direction. Balme and his colleagues hope to link the presence of dust devils to any local "twists" in the wind that get detected by the stations.

Tornadoes and other major storm systems are fueled by regional temperature differences. But dust devils are much more local. They develop when ground temperatures are warmer than the surrounding air. The rising warm air creates a swirling vortex column that catches up dust and other particles as the whole setup races across the desert, typically at just a few miles per hour.

To uncover more about the elusive dust devils, chase teams of two to six people will race ahead of a dust devil at 40 to 50 mph (64 to 80.5 kph) before getting in its path and slamming on the brakes. That's the signal to use a modified winch on their truck's front end to lower a sensor package that can gauge pressure, temperature and dust-amounts as the dust devil passes overhead.

The swirling vortexes can appear up to 130 feet (40 meters) across and almost two-thirds of a mile (1 km) up, making a strange sound between a roaring noise and gentle sigh.

"Coming toward you it's quite threatening," Balme told SPACE.com, describing his first experience waiting on a dust devil. However, the dust devil did nothing more than ruffle his hair and throw some dust grains in his face.

A bigger problem comes from dust devils proving, well, devilish. Balme has seen dust devils come right up to the truck before heading off in a different direction, leaving the team scrambling to raise their sensor package within a few seconds and go tearing off again.

One team will hunt dust devils near Eloy, Arizona, while another team spends time around Nevada's Eldorado Valley. The different climate areas should help provide a better understanding of how dust devils can arise even in the cold landscape of Mars.

Big differences

The NASA-backed study will also allow Nilton Renno, an atmospheric scientist at the University of Michigan and member of the Phoenix Mars Lander team, to test climate model equations that try to describe how dust devils form.

"Rather than just stamp-collecting lots of measurements of dust devils, we're actually going to try and tie them to what's going on in the local climate," Balme said.

Some changes become necessary to adapt the data to a Mars model. For instance, the maximum spin velocity of dust devils on Earth is about 50 mph (80.5 kph), while dust devils on Mars may spin up to 200 mph (322 kph) because of the thin atmosphere. Dust devils there are known to soar six miles (10 km)  into the atmosphere.

Improved climate models should help better understand the whirling dervishes of Mars, at least until future missions can obtain more direct measurements.

"It was such a shame when we saw the beautiful MER [Mars Exploration Rover] pictures," Balme noted. "I was thinking that all we need is a little wind sensor."

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• Images: Phoenix on Mars!