Many areas on Mars experience the passage of giant dust devils. These dust devils leave tracks on the surface of Mars because they disturb a thin coating of fine bright dust that covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface. Within a few weeks, the dark track assumes its former bright colour, either by being re-covered through wind action or due to surface oxidation through exposure to sunlight and the Martian atmosphere.
Formation and dynamics
Dust devils occur when the sun warms up the air near a flat, dry surface. The warm air then rises quickly through the cooler air and begins spinning while moving ahead. This spinning, moving cell may pick up dust and sand and leave behind a clean surface.
Observation
Dust devils on Mars have been photographed both from the ground and high overhead from orbit. They have even blown dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime. The pattern of the tracks has been shown to change every few months. A study that combined data from the High Resolution Stereo Camera and the Mars Orbiter Camera found that some large dust devils on Mars have a diameter of and last at least 26 minutes. Measurements from the Curiosity Rover confirms that the pressure drops when a dust devil passes nearby.
Changes through time
A dust devil that was previously imaged in 2009, there was information found about two years later showing the tracks visible from the previous imaging are completely different from the old ones meaning there had been a dust storm to erase the old tracks. Since it is not always too easy to observe these dust devil tracks on Mars tests have been done on Earth to further our understanding of these storms. Traditionally dust devils leave tracks that are darker, but satellite images have captured some cases where they are lighter than the traditional markings. In conclusion the marks were not darker than usual but the sand had been darkened by five minutes of rainfall during the previous night. Since there is no proof of water on Mars indefinitely it is believed that these lighter marks are being held together by electrostatic forces.
