NASA says it is monitoring a massive dust storm on Mars that has produced atmospheric changes.
It's the first time since the 1970s that NASA is studying such a phenomenon both from orbit and with a weather station on the surface, the US space agency said on its website.
"This is now a regional dust storm," said Rich Zurek, chief Mars scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. "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."
Regional dust storms expanded and affected vast areas of the Red Planet in 2001 and 2007.
"One thing we want to learn is why do some Martian dust storms get to this size and stop growing, while others this size keep growing and go global," said Zurek.
Following decades of observations, experts know there is a seasonal pattern to the largest Martian dust storms, according to NASA. The most recent dust storm season began just a few weeks ago with the beginning of spring in the southern hemisphere.
As of November 16, the Mars Reconnaissance Orbiter detected a warming of the atmosphere about 25 kilometres above the storm. Since then, the region's atmosphere has increased about 25 degrees Celsius.
The phenomenon is due to dust — being lofted above the surface — absorbing sunlight at that height, according to NASA.
Warmer temperatures have also been detected in a "hot spot" near northern polar latitudes due to changes in atmospheric circulation.
The storm, which came no closer than about 1350 kilometres to NASA's Opportunity robot, on Mars since 2004, resulting in a "slight drop in atmospheric clarity over the rover", NASA said.
If the storm continues to spread out, Opportunity could be affected since it depends on solar energy for its power supply.
"More dust in the air or falling onto its solar panels would reduce the solar-powered rover's energy supply for daily operations," NASA said.
NASA's Mars rover Curiosity, which arrived on Mars on August 6 and is powered by a radioisotope thermoelectric generator rather than solar cells, is likely to be less affected.
"The main effects of increased dust in the air at its site would be haze in images and increased air temperature," said NASA.
Curiosity's weather station — located halfway around the planet from Opportunity — detected atmospheric changes tied to the storm, with sensors measuring a decrease in air pressure and a slight rise in overnight low temperature.
Curiosity is on a two-year, $US2.5 billion mission to investigate whether it is possible to live on Mars and to learn whether conditions there might have been able to support life in the past.