May 29, 2005
Spirit Captures the Bluster on Mars
The tiny tornadoes, or dust devils, that scientists have observed from orbit have now been seen close up on the surface by the Spirit rover. The most recent series of images show that these tornadoes can appear suddenly with diameters in the hundreds of feet.
Astrobiology Magazine -- A dust devil spins across the surface of Gusev Crater just before noon on Mars. NASA's Spirit rover took the series of images in this 21-frame animation with its navigation camera on the rover's martian day, or sol, 486 (March 15, 2005).The event occurred during a period of 9 minutes and 35 seconds beginning at 11:48 a.m. local Mars time, recording the dust devil's progress in a northeasterly direction about 1.0 kilometer (0.62 mile) away from Spirit's perch on the slopes of the "Columbia Hills." The whirlwind was traveling at about 4.8 meters per second (16 feet per second) and covered a distance of about 1.6 kilometers (1 mile).
Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil. The dust devil is about 34 meters (112 feet) in diameter.
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 Shane Thompson, Research Technician with the Planetary Geology Group at Arizona State University.
"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."
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