NASA recently published a wonderful close-up image of Mars (Fig. 1), acquired by the Mars-bound MRO spacecraft. The image shows a huge Martian dust devil, a type of whirlwind, roughly 20 km high. The dust devil was photographed while swirling along a Martian plain, on 14 March 2012, by a sophisticated camera on MRO. Despite its height, the dust whirl was only a little more than 70 m across.
Dust devils, occur on Earth as well as on Mars. They are spinning columns of air, made visible by the dust they carry. Unlike a tornado, a dust devil usually forms on a clear day, when the ground is heated by the Sun, warming the air immediately above the ground. As warm air near the surface rises quickly through a small pocket of cooler air above it, the air may begin to rotate, if conditions are just right.
MRO was launched toward Mars in August 2005, and reached Mars orbit in March 2006. The Mars-orbiting probe continues to yield insights into the Red Planet's ancient environments and how processes such as wind, meteorite impacts and seasonal frosts continue to affect the Martian surface today. The MRO mission has obtained more data about Mars than all other orbital and surface missions combined.
Further Reading
http://www.nasa.gov/mro
References
NASA
www.nasa.gov/
Wikipedia