A huge Martian dust storm tracked from orbit by NASA has affected both Curiosity and Opportunity, the agency's active rovers on the planet's surface.

Stitched together shot of Mars during the storm. Credit: NASA/JPL-Caltech/MSSS

The Mars Reconnaissance Orbiter circling above the red world picked up the huge storm twelve days ago and reported it to NASA's rover teams. Dust storms on Mars are rare, but sometimes cover huge areas or even the entire planet.

"This is now a regional dust storm. It has covered a fairly extensive region with its dust haze, and it is in a part of the planet where some regional storms in the past have grown into global dust hazes," says Rich Zurek, chief Mars scientist at NASA's Jet Propulsion Laboratory.

"For the first time since the Viking missions of the 1970s, we are studying a regional dust storm both from orbit and with a weather station on the surface."

Sensors on the newly-arrived Curiosity, halfway round the planet from the storm, are showing decreased air pressure and a slight rise in overnight low temperature.

For its part the veteran Opportunity prowler was slightly obscured from space by the dust from the storm. The rover doesn't have its own weather station but boffins are watching its readouts anxiously.

Martian dust storms have to be monitored to protect the rovers on the planet. If a storm goes global, Opportunity would be in the most trouble. Dust in the air or on its solar panels could deplete the rover's energy supply, possibly flatlining it altogether as happened with its companion, Spirit, when it got trapped in a sandpit and couldn't align its solar panels correctly for survival through the Martian winter.

Curiosity is nuclear powered and would not suffer any power loss, but dust in the air where it is would haze images and increase the air temperature.

Regional dust storms affected vast areas of Mars in 2001 and 2007, but not since then. From decades of study, boffins know there is a seasonal pattern to the largest dust storms, but not why some of them get so big.

The orbiter has detected this storm warming the atmosphere, increasing the temperature by 25 degrees Celsius so far, as the dust absorbs the sunlight around 16 miles above the storm. There's also a hot spot near the northern polar latitudes due to changes in atmospheric circulation. ®