Surveyor Spots Bright Sand Dunes On Mars

February 18, 1999

ITHACA, N.Y. -- After analyzing hundreds of high-resolution pictures of the Martian surface taken by the orbiting Mars Surveyor spacecraft, a team of researchers finds that weathering and winds on the planet create landforms, especially sand dunes, remarkably similar to those in some deserts on Earth.

Newly identified smaller, bright sand dunes, the researchers speculate, are formed of sulfates, possibly gypsum. These dune fields, which are a few miles across, appear bright in photographs because of the way in which the sand particles reflect light. The much larger dark dune fields, up to tens of miles across, are most likely made of grains eroded from lava flows.

At certain times of the Martian year the winds are strong enough to move these sand particles to many areas of the now-dry planet.

"We can see from the high resolution that the winds are sorting these different particles out and they haven't been homogenized with the rest of the planetary dust. In one picture we can actually see the bright stuff blowing off the dunes," says Peter C. Thomas, a senior researcher at Cornell University's Center for Radiophysics and Space Research. Thomas and his colleagues, including Joseph Veverka, Cornell professor of astronomy, present their findings on the shifting dunes of Mars in this week's issue (published Feb. 17) of the journal Nature.

Thomas speculates that an observer standing amid the sand dunes would be "sand blasted" at particular seasons of the year as the winds moving through the thin Martian atmosphere whip the particles along at tremendous velocity. But at other seasons of the Martian year, he says, "there would be nothing blowing at all."

The researchers studied high-resolution pictures taken by the Mars Orbiter Camera (MOC) on board the Mars Global Surveyor spacecraft, which took images periodically while shrinking its orbit toward the final mapping orbit reached this month. The spacecraft, which entered Mars orbit in September 1997, now takes 118 minutes to circle the planet. The MOC takes images of the surface with a resolution as much as 50 times greater than the previously available pictures taken by the Viking spacecraft more than two decades ago.

In many of the hundreds of pictures studied, says Thomas, the dark sand dunes, which were also visible in the Viking pictures, are sharply etched. But on eight of the images, much brighter dunes, only hinted at in one or two blurry Viking images, also are clearly visible. "We don't really know the composition of the bright dunes but we are inferring sulfates because Viking and other data showed a lot of sulfates in the Martian soil. Gypsum would be bright and soft enough to erode quickly downwind as the images indicate," says Thomas. However, he adds, the bright dunes could be formed of particles cemented by sulfates, or other minerals.

The winds on Mars appear strong enough to transport sand only at certain times of the year. A major reason is the planet's eccentric orbit, which produces strong winds primarily when Mars is closest to the sun. Strong winds also are due to the fact that a third of the atmosphere falls out of the carbon dioxide polar caps, and the motion of the gas creates very strong, highly seasonal and one-directional winds at high latitudes.

Until now, says Thomas, the model of the Mars atmosphere "was one of winds moving sand not very often and then pretty much in one direction at a particular spot -- and that's exactly what we are seeing." On a broad level, he says, modelers of the Martian atmosphere have the picture right.

As on Earth, the winds are selective in the particles they transport, by mass and composition. Much of the red planet is blanketed in a ubiquitous layer of dust, probably composed of rusty mixtures of clays and iron oxides. In certain areas, though, says Thomas, the wind is "cleaning off this dust" and replacing it with other particles to create the bright dunes.

The sulfates, he speculates originally could have come from weathering in ancient dry river and lake beds, from groundwater or from hot springs.

Other authors of the Nature paper are M.C. Malin of Malin Space Science Systems, San Diego; M.H. Carr and L.A.Soderblom, U.S. Geological Survey; G.E. Danielson and A.P. Ingersoll, California Institute of Technology; M.E. Davies, the Rand Corp.; W.K. Hartmann, Planetary Science Institute, Tucson; P.B. James, University of Toledo; and A.S. McEwen, University of Arizona. The research was funded by NASA.

Cornell University

Related Mars Articles from Brightsurf:

Water on ancient Mars
A meteorite that originated on Mars billions of years ago reveals details of ancient impact events on the red planet.

Surprise on Mars
NASA's InSight mission provides data from the surface of Mars.

Going nuclear on the moon and Mars
It might sound like science fiction, but scientists are preparing to build colonies on the moon and, eventually, Mars.

Mars: Where mud flows like lava
An international research team including recreated martian conditions in a low-pressure chamber to observe the flow of mud.

What's Mars made of?
Earth-based experiments on iron-sulfur alloys thought to comprise the core of Mars reveal details about the planet's seismic properties for the first time.

The seismicity of Mars
Fifteen months after the successful landing of the NASA InSight mission on Mars, first scientific analyses of ETH Zurich researchers and their partners reveal that the planet is seismically active.

Journey to the center of Mars
While InSight's seismometer has been patiently waiting for the next big marsquake to illuminate its interior and define its crust-mantle-core structure, two scientists, have built a new compositional model for Mars.

Getting mac and cheese to Mars
Washington State University scientists have developed a way to triple the shelf life of ready-to-eat macaroni and cheese, a development that could have benefits for everything from space travel to military use.

Life on Mars?
Researchers from Hungary have discovered embedded organic material in a Martian meteorite found in the late 1970s.

New evidence of deep groundwater on Mars
Researchers at the USC Arid Climate and Water Research Center (AWARE) have published a study that suggests deep groundwater could still be active on Mars and could originate surface streams in some near-equatorial areas on Mars.

Read More: Mars News and Mars Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to