At around 10 o'clock Mars-time on a recent morning, pockets of cooler and warmer air varying by as much as 7 degrees Fahrenheit (4 degrees Celsius) drifted past the rover.

Ride the thermals

The changes are probably generated by a process similar to what occurs on Earth, when the Sun heats the surface, pockets of warm air rise, and cooler air drops to the surface in other locations, explained Cornell University's Don Banfield.

These same thermals, as they are called, allow eagles to soar without flapping their wings.

All the while, Opportunity found, wind blows the air pockets along the planet's surface. The warm pockets rise to about 330 feet (100 meters). Higher up, temperature differences are less extreme.

The rover can measure air temperature every two seconds with its Mini-TES infrared instrument, using a complex technique scientists hadn't considered until the robot was deployed at Mars.

At a press conference yesterday at NASA's Jet Propulsion Laboratory, Banfield described "huge jumps" in temperature occurring every minute or so.

"If you could live on Mars you could probably feel this temperature change," Banfield said. "This is a significant temperature change."

Further investigation should improve understanding of the air on Mars, as well as how it sculpts dunes and causes erosion by blowing sand grains about.

Future mission planners will be eager for the results. When Opportunity's twin, Spirit, was about to land in early January, it was buffeted by strong wind gusts. Onboard thrusters fired to keep the craft in a proper attitude.

More study planned

Daytime temperatures near the Martian equator, where Opportunity is, can climb above zero. But the atmosphere is only about 1 percent as dense as Earth's, so at night temperatures plunge to around -130 Fahrenheit (-90 Celsius).

The 1997 Pathfinder saw hints of the strong temperature variations, said Mark Lemmon, a member of the rover science team from Texas A&M University. But Pathfinder only measured temperatures up to 5 feet (1.5 meters) from the surface.

Opportunity uses its infrared spectrometer to detect differences in heat up to 3 miles (5 kilometers), Banfield said. Fortuitously, NASA's orbiting Mars Global Surveyor (MGS) has a similar instrument that can gauge temperature down to about 3 miles above the surface.

This weekend, Banfield said, MGS will fly over Opportunity, and scientists plan to point the two instruments at each other. The result will be the first-ever temperature profile of a patch of Martian atmosphere from the surface all the way up to its outer reaches.

http://www.space.com/scienceastronomy/martian_winds_040213.html