Malin Space Science Systems.

Evidence that the sand dunes of Mars are moving might, over time, allow measurement of the wind erosion on the planet. The dune field, called Proctor Dunes, shown in this latest Mars Global Surveyor image shows evidence of recent activity, as dark sand has been moved across surfaces covered by the late-winter remains of seasonal frost.

Does Mars have shifting sands? Over the past few months the camera on board the Mars Global Surveyor has provided tantalizing evidence of surface changes on the planet as sand dunes that cover large areas show signs of being moved by the Martian wind.

The latest photographic evidence -- the sharpest Mars images to date -- says Cornell University astronomer Peter Thomas, indicates that the surface of Mars is "dynamic" and that the dunes have indeed been active in the few months since frost was deposited on the surface.

"This is a major finding, and through the use of this very high-resolution camera we now see real action of the geological features. This has tied current wind conditions to geological features," Thomas said.

Thomas, a member of the Mars Global Surveyor camera team and a senior researcher in the Cornell astronomy department, commented at a NASA Space Science Update today (Aug. 10, 1999) at NASA headquarters in Washington, D.C. Other presenters in the briefing, which was broadcast via satellite on NASA television, included Michael Malin of Malin Space Science Systems, San Diego, principal investigator for the Mars Orbiter Camera instrument on the Surveyor; Jim Zimbelman, planetary geologist in the Center for Earth and Planetary Studies at the Smithsonian Institution's Air & Space Museum, Washington, D.C.; and Michael Meyer, Mars Surveyor 2001 program scientist in NASA's Office of Space Science.

The Mars researchers released pictures that will enable further study of these dynamic features in greater detail than ever before. Since they were first seen in Mariner 9 images of Mars from the early 1970s, the dune fields have been of great interest to researchers because of the indication that the sand is moving. Evidence of such changes would make it possible to measure the effectiveness of wind erosion on Mars.

Mars is a sufficiently different place today than it was two years ago when the Global Surveyor first arrived, and the new images show that the planet's weather and dust play a major role in changing the way it looks. The spacecraft's wide-angle cameras monitor the planet's weather on a daily basis, just like weather satellites above the Earth. The Martian weather has been particularly active during the past two months as spring arrived in the southern hemisphere and autumn approached in the north.

Thomas noted that researchers do know that frost itself can be blown around by wind, "but we would like to find evidence that landforms beneath are active." Now, he said, the camera has shown at a few meters' resolution "that things do move as soon as you get frost off the dunes."

One image of sand dunes just three kilometers across showed streamers of dark sand moving over the frost, Thomas said, "proof positive that sand is moving at present. This isn't just fossil landforms sitting there, having frost come and go, but there are real active dunes on the surface of Mars."

He characterized this finding as "an important question for putting all of Mars geology in context in relation to the present climate." Summing up, he said the new images show that for researchers Mars "has become a full-fledged, fully respectable planet in terms of the great variety of geologic features all over the surface. "

Mars Global Surveyor carries five science instruments designed to generate a complete global portrait of Mars and its seasonal changes during a full Martian year, the equivalent of two Earth years. The spacecraft entered its primary circular mapping orbit in February, and is just beginning its second full Martian year in orbit around the red planet.

Global Surveyor is the first mission in a long-term series of Martian explorations known as the Mars Surveyor Program, which is managed by the Jet Propulsion Laboratory for NASA.