14 DAY TRIAL // Due to the fact that Mars is about half the diameter of the Earth and has a gravity about six times weaker than ours, the Red Planet has a relatively thin atmosphere compared to our own. The researchers show that, for a sand dune to move across the Martian surface just a meter, it might take up to 1,000 years, mostly because of the absence of liquid water running across its surface and the action of strong winds.
Using computer simulations to reproduce the conditions on the surface of Mars, Parteli, a researcher at the University of Stuttgart in Germany and a colleague, Hans Hermann of Brazil's Federal University of Ceara, observed some dunes similar to those photographed by the Mars Orbiter. These images were taken by the Mars Global Surveyor spacecraft before the end of its mission last year, after ten years of studying the planet's surface.
The results of the simulations showed that to create a sand dune one meter tall, the wind would have to blow at a speed of 120 kilometers per hour, for it to move appreciably. Though the Red Planet has an unstable spin axis and winds at such speeds are extremely rare and occur only a few times in a decade, thus the movements of the sand dunes are greatly restricted mainly due to the thin Martian atmosphere.
This evidence can be seen all over the Earth's surface, where sand dunes are frequently shaped by water and winds. So far, the effort to find liquid water on the Red Planet with the help of surface rovers and space surveyors had no concluding result.
Dunes similar to those present on Earth can be seen on the Martian surface, though not as high as ours. Sand dunes on Mars can reach up to 6 meters in height and seem to have more of a crescent shape and they are also transverse, while the long, sinewy linear dunes are most common on Earth.
Though the Mars atmosphere is about one hundred times thinner than that on Earth, it can produce sand storms from time to time, such as that which partially covered the solar cells of the Spirit and Opportunity rovers this summer, forcing Spirit to move to a more angled slope to maximize its light capturing capacity.
According to Parteli, if the sand moving winds on Mars occurred as frequently as those on Earth, the sand dunes would be moving ten times faster across its surface, due to its weak gravity. Simulations also show that winds strong enough to create a bimodal dune would need about 50,000 years to create such a structure. Nevertheless winds on Mars change directions in a few hours, but are not strong enough to move sand.