This movie clip shows a single dust devil -- a whirlwind that lofts dust
into the air -- about 2 kilometers (1 mile) away, moving across a plain
inside Mars' Gusev Crater for several minutes. The dust devil appears in
21 frames. The number of seconds elapsed since the first frame is
indicated at lower left of the images, typically 20 seconds between
frames. The navigation camera on NASA's Mars Exploration Rover Spirit
took these images on the rover's 445th martian day, or sol (April 14,
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.
