Originally created 12/10/97

Global Surveyor sees Atlantic-sized dust storm brewing on Mars



SAN FRANCISCO -- Brand-new images show a dust storm covering 20 percent of Mars, forcing controllers to make some small adjustments in the Mars Global Surveyor's orbit.

The storm brewing in the planet's southern hemisphere was first detected more than two weeks ago.

"We don't know yet whether it will grow into a global dust storm or will diminish," project scientist Arden Albee told reporters Monday at the annual meeting of the American Geophysical Union.

However, given the storm's holding pattern in the last couple of days, Michael Malin, the top Global Surveyor camera scientist, doubts it will spread globally.

"The storm has not gone global and is not likely to go global," Malin said. In images captured Sunday, the area of dustiness extends from around 35 degrees south all the way to the pole.

But the dust storm "is not extending to the northern hemisphere," he said.

Global Surveyor, with its bird's-eye view of the planet, is giving scientists the best look yet at how the martian climate and atmosphere behave. Despite a damaged solar panel that forced a redesign of the mission, the craft is returning an unexpected bonanza of data.

Albee and Malin said Surveyor instruments are seeing a dustier atmosphere, which is hotter because it absorbs more sunlight. The hotter atmosphere swells and increases atmospheric pressure, which is an issue for how controllers adjust the spacecraft's orbit.

The spacecraft has been using a technique called aerobraking, which takes advantage of atmospheric drag, to trim its orbit from an ellipse into an eventual circle. Controllers have been gradually lowering it into the planet's atmosphere since mid-September.

According to Albee, of the California Institute of Technology in Pasadena, the denser atmosphere has forced controllers to make small adjustments and raise the orbit by about 3 miles at a time in recent days to avoid stressing Surveyor's damaged solar panel.

Global Surveyor arrived at the red planet in September in the shadow of the much-heralded Mars Pathfinder. It has returned some striking findings on early orbits well in advance of when it will begin mapping the planet in March 1999, scientists said.

"We are finding changes from one orbit to the next," Albee said.

Malin, of Malin Space Science Systems in La Jolla, said the images are "really changing our understanding of Mars. Our understanding of Mars dust storms and Mars climate will skyrocket."

For example, he said that there are layers of dusty haze about 37 miles up in the northern atmosphere while dust storms are permeating reaches of the southern hemisphere. Although scientists don't yet have an explanation for the observation, it implies there is some sort of global circulation of the planet's atmosphere.