This picture shows 2 images by Hubble Space Telescope, taken about a month apart in 1996. It shows an active dust storm near the edge of the Martian north polar cap. The dust storm is about the size of an average state in the USA.
This polar storm is probably a consequence of large temperature differences between the polar ice and the darker region close to the ice cap.
The photograph at the top shows a 1,000 kilometer long dust storm on the north polar cap of Mars. Part of this dust storm can also be seen in the darker area close to the ice cap - at the bottom of the photograph. The photograph at the bottom shows the dust storm one month later: broken up and looking like a comma.
Image credit: Phil James (University of Toledo), Steve Lee (University of Colorado) and NASA
Picture of a global dust storm on Mars. When the Hubble Space Telescope took this picture in September, the dust storm had already been raging across the planet for nearly two months obscuring all surface features. Such seasonal global dust storms on Mars is common. However, this is the biggest storm seen in the past several decades.
Both images are in natural color, taken with Hubble's Wide Field Planetary Camera 2.
Image Credit: NASA, James Bell (Cornell Univ.), Michael Wolff (Space Science Inst.), and the Hubble Heritage Team (STScI/AURA)
The dust devil in this picture was traveling from right to left. Sunlight coming from the upper left (in the picture) casts a shadown in the shape of a column. This shadow indicates the true shape of this dust devil (and dust devils in general).
The dust devil itself (bright area on the left) does not look like a column because the picture was taken from directly above the dust devil. The dust devil is less than 100 meters wide. This picture covers an area approximately 1.5 by 1.7 kilometers wide.
Photo Credit: NASA/JPL/Malin Space Science Systems
This picture shows dark streaks on the rippled flats of Argyre Planitia. ( Map of Mars ). The picture covers an area of 3 km by 5 km.
(Planitia means a lowlying plain or large, relatively featureless lowlands)
Some streaks are straight and narrow, others are curly arcs, twisty, and loopy. Dust devils make these dark streak by removing bright dust from the terrain in its path, thereby revealing the darker surface of Mars underneath.
The picture on the right shows close-up detail of the central part of the picture on the left.
Photo Credit: NASA/JPL/Malin Space Science Systems
Dust devils look somewhat like miniature tornadoes. They are spinning, columnar vortices of wind that move across the Martian landscape and pick up dust.
Dust devils are a common occurrence in dry and desert landscapes on Earth and Mars. Dust devils generally form during the day. The hot ground warms the air immediately above its surface. This hot air closest to the surface begins to rise, and starts to spin. This spinning column begins to move across the surface and picks up loose dust (if present).
The dust makes the vortex visible and gives it the 'dust devil' or tornado-like appearance. In this picture the shape of the dust devil is best seen in the shadow it casts. Based on the length of its shadow, the dust devil in this photograph is about 1 kilometers high.
