Tornado, Signs of Martian Spring
|Fortuitous afternoon timing of an unpredictable atmospheric event had proven elusive to ground controllers of the Spirit rover until around March 10.|
What started out as a couple of dust devils first spied by the Spirit rover a couple of weeks ago has now turned into a swarm of dust devils wheeling across the plains of Gusev Crater almost every day.
So far, the dust devils are about the same size as those that whip up desert dust and sand in the southwestern United States, though orbital images in past years have detected dust devils in many places on Mars that are up to several kilometers (a few miles) tall, says Shane Thompson, Research Technician with the Planetary Geology Group at Arizona State University.
NASA’s Spirit rover spotted the first dust devil of the Mars Exploration Rover mission on martian sol, or day, 421 (March 10, 2005). The dust devil was observed the day after martian winds cleared the rover’s deck and increased the amount of power the rover harvested from sunlight shining on its solar panels.
Rover science team member Ron Greeley, Director of the Planetary Geology Group, has been tracking and studying dust devil characteristics in detail on both Mars and Earth for the past couple of years. Scientists believe the small cyclones are seasonal, perhaps linked to wind storms that occur in the martian spring.
"We’re trying to determine whether dust devils play a small or large role in changing the surface of Mars in the short-term," says Thompson.
|Active Martian dust devil caught in the act of creating a sandblast track in Promethei Terra, December 11, 1999.|
Credit: NASA/JPL/Malin Space Science Systems
"At the Pathfinder site during its 83 sol mission, approximately thirty dust devils were either sensed by the pressure drop as they passed over the lander, or were imaged by the Pathfinder camera," says Peter Smith of the University of Arizona (Tucson). "Based on these observations, one might expect to see several dust devils per hour from an active site on Mars between 10 am and 3 pm. Few, if any dust devils will be present at other times. Dust devils typically form during late spring and summer and can be found at all latitudes. Exactly, how their population density varies around the planet is currently unknown."
In addition to Pathfinder’s run-in with a dust devil, previous missions to Mars have run into very dusty days. For instance, there was a dust storm covering the Viking Lander I (VL-1) site on Martian day (1742) or sol 1742 (1 Martian year=669 Earth days). In 1971, Mariner 9 and 2 USSR missions all arrived during a dust storm.
"Rovers and other robots must be carefully designed to withstand the sandblasting that they will endure from dust devils," said Smith. "Bearing surfaces and solar panels must be protected and dust accumulation on solar panels will lower their efficiency."
Dust devils, have been caught in the act by orbital cameras before. These miniature tornadoes can span about 10 to 100 meters wide with 20- to 60-mile-per-hour (32- to 96-km/hr) winds swirling around a heated column of rising air. One might expect to see several dust devils per hour from an active site on Mars between 10 am and 3 pm, when rising afternoon air is hottest.
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