This movie clip shows a single dust devil -- a whirlwind that lofts dust into the air -- that passed near the bottom of the hillside where NASA's Mars Exploration Rover Spirit was located at the time. A shorter clip of the same dust devil was release previously [PIA07861], but an additional frame of the sequence was sent later by the rover. The proximity of the dust devil makes this sequence the best obtained so far for showing details of its structure. Spirit's navigation camera took these images on the rover's 446th martian day, or sol (April 15, 2005.) Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil.
Scientists expected dust devils since before Spirit landed. The landing area inside Gusev Crater is filled with dark streaks left behind when dust devils pick dust up from an area. It is also filled with bright "hollows," which are dust-filled miniature craters. Dust covers most of the terrain. Winds flow into and out of Gusev crater every day. The Sun heats the surface so that the surface is warm to the touch even though the atmosphere at 2 meters (6 feet) above the surface would be chilly. That temperature contrast causes convection. Mixing the dust, winds, and convection can trigger dust devils.