A Mid-Summer's Dust Devil
One objective for the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in
the Extended Mission is to continue looking for changes and dynamic events taking
place on the red planet. The feature shown here elicited gasps of exitement among
the MOC Operations Staff when it was received in early April 2001.
The feature is a dust devil. Dust devils are spinning, columnar vortices of wind that
move across the landscape, pick up dust, and look somewhat like miniature
tornadoes. Dust devils are a common occurrence in dry and desert landscapes on
Earth as well as Mars. When this dust devil was spied in Amazonis Planitia on April
10th, the MOC was looking straight down. Usually when the camera is looking down
the dust devil will appear as a circular, fuzzy patch with a straight shadow
indicating its columnar shape. In this case, however, the dust devil is somewhat
curved and kinked---its shape is best seen in the shadow it casts to the right. A
thin, light-toned track has been left by the dust devil as it moved eastward across
the landscape. Usually, such tracks are darker than the surroundings, in this case
the light tone might indicate that the dust being removed by the passing dust devil
is darker than the surface underneath the thin veneer of dust.
Dust devils most typically form when the ground heats up during the day, warming
the air immediately above the surface. As the warmed air nearest the surface
begins to rise, it spins. The spinning column begins to move across the surface and
picks up loose dust (if any is present). The dust makes the vortex visible and gives
it the "dust devil" or tornado-like appearance. This dust devil occurred at an
optimal time for dust devils whether on Earth or Mars---around 2 p.m. local time in
the middle of Northern Hemisphere Summer. North is up, sunlight illuminates the
scene from the left (west), and 500 meters is about 547 yards. The shadow cast by
the dust devil goes off the edge of the image, but the length shown here (about 1.5
km) indicates that the dust devil was a bit more than 1 km (0.62 mi) in height.
Images Credit: NASA/JPL/Malin Space Science Systems
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