Space

Dark sand dunes on Mars resemble the ripples on chocolate candy bars in a recently released image taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter spacecraft.

The dunes lie on the floor of a 300-kilometre-wide crater called Herschel. The structures, called barchan dunes, are often found in sandy deserts on Earth.

Researchers suspect the steep-faced dunes on Mars are composed of basaltic sand. Their grooved texture indicates that the sand may have been cemented together somehow and then sculpted into crescent shapes by the wind. Their orientation reveals that the strongest wind in the region blows from north to south.

The dunes are not a new discovery. NASA's Mars Global Surveyor also took a picture of this dune field in 2001.

In 2004, planetary scientists from Oberlin College in Ohio and Oklahoma State University in Stillwater, both in the US, said the dunes were probably formed during summers on the planet's southern hemisphere.

At that time, Mars is 20% closer to the Sun than it is in other seasons, providing more energy that can drive stronger winds on the planet.

HiRISE, the most powerful camera ever sent to Mars, snapped its pictures from 259 kilometres above the dunes when it passed overhead on 7 March.

The Mars Reconnaissance Orbiter has been circling Mars since March 2006 (see New Mars probe safely enters orbit). Since then, it has returned data on new gullies, old spacecraft and possible underground water pipes on Mars.

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