Researchers used the navigation camera on NASA's Mars Exploration Rover Spirit to look for dust devils near the rover during the mission's 1,919th Martian day, or sol (May 27, 2009). This shot from that day's sequence, presented here with three different levels of processing, caught a large dust devil about 1.5 kilometers (1 mile) northwest of Spirit.
The top frame is the original image, the middle frame has been processed enhance the visibility of the dust devil, and the bottom frame is a merged version. The image was taken in the early afternoon from Spirit's position at the "Troy" sand trap beside "Home Plate," looking northwest across the floor of Gusev crater. The large dust devil shows a typical central core (brightest area) surrounded by a more diffuse sand and dust "skirt" about 415 meters (about 1,350 feet) across. The dust devil is moving toward the northeast (toward the right in this image) at about 0.75 meter per second (1.7 miles per hour). This dust devil is some 20 times larger than the average dust devil on Earth. A smaller dust devil is seen on the right leading the larger dust devil.
More than 650 dust devils have been recorded by Spirit since its operation began in 2004. The mission is currently in its third "season" for dust devils on Mars, which typically begin in Martian spring.
Dust devils occur on both Mars and on Earth when solar energy heats the surface, resulting in a layer of warm air just above the surface. Since the warmed air is less dense than the cooler atmosphere above it, it rises, making a swirling thermal plume that picks up the fine dust from the surface and carries it up into the atmosphere. This plume of dust moves with the local wind.