This observation shows sand dunes within the Hellespontus region of Mars.

The sand appears to come from the layered mesas and knobs, features that have been eroded by powerful winds. The dunes here have a morphology indicating formative winds blowing from east to west (from right to left).

The primary indicator for this is the orientation of the barchan dunes, a dune type that on Earth has its horns in the downwind direction. Also, the steepest faces of the dunes are on the dunes’ eastern side, indicating easterly winds.

In addition to the barchans, some of the dunes are organized into a “seif,”, or longitudinal, form whereby their long axis is parallel to the wind. These are seen emanating from the sand sheets next to the mesas and knobs, as well as from some barchan horns.

Mystery of Mars' Sand Dunes Solved

A long-standing mystery about Mars' sand dunes may have just been sold by scientists. The strange thing about the dunes is that they look as if they were created by winds, but there are no winds on the surface of Mars.

Discovered in 1971 in pictures taken from space, above the surface, they look very similar to sand dunes on Earth, so they must have been created through the same processes as in our deserts. However, how could winds have been causing them when the Martian atmosphere is so thin and still?

Many consecutive missions to Mars have detected no change in the position and sizes of the dunes, unlike the dunes on Earth, which are shifting constantly. Astronomers now found out that they really have been formed by the action of winds, only that winds on Mars are moving so slowly that they're virtually undetectable, meaning that the dunes were formed far more slowly than back on Earth, like in a movie seen in slow motion.

Eric Parteli at the University of Stuttgart and Hans Herrmann at the Swiss Federal Institute of Technology in Zürich has performed a series of computer simulations of the formation of two distinct types of dunes seen on Mars: the arrowhead-shaped "barchan" dunes, (formed when the wind blows mainly in one direction), and elongated "exotic" dunes (formed when the wind alternates between two directions).

The formation process has also been explained, and it's called "saltation," which means a small grain of sand is lifted by the wind, and driven along above the sand until it falls back, creating a splash of ejected grains. The ejected grains could then also be picked up by the wind leading to a rapid multiplication of the amount of sand that is being blown along.


Results also shown that the dunes on Mars do shift, only that they do it far too slowly for us to detect their movement, which is estimated at 1 meter (0.3 ft) every 4000 years.