March 13, 2000
Since Mars Global Surveyor arrived in September 1997, its high-resolution camera has been snapping pictures of puzzling dark streaks and lines that seemed to defy simple explanation -- until now. In December 1999, scientists had their first solid evidence, a picture of a dust devil caught like a graffiti artist in the act of etching the surface of Mars.
"Dust devils are spinning columns of air that move across the landscape and look somewhat like miniature tornadoes," said Dr. Ken Edgett, a staff scientist at Malin Space Science Systems, San Diego, CA. "We've captured them in the midst of sweeping up dust and leaving behind a dark streak. This is the 'smoking gun' that explains the wild, sometimes twisted 'spaghetti' of dark streaks and trails we have been seeing. I get the feeling when I look at these pictures that something is 'moving'. These things send shivers down my spine."
Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. They form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust. The dust makes the vortex visible and gives it the "dust devil" or tornado-like appearance. On Earth, dust devils typically last for only a few minutes and the same is probably true for Mars.
"What is exciting about this dust devil finding is that we are witness to one of the processes that help explain cause of some of the seasonal variations in the bright and dark surfaces on Mars. The dust devils remove some of the bright dust and cause the surfaces to appear to darken in the spring and summer seasons. Each little dust devil that runs across the landscape makes the surface in that region just a little bit darker," Edgett explained. "This isn't happening everywhere, but it seems to be most common in the mid-latitudes of Mars. In recent weeks, we have seen as many as five to 10 devils at a time running across the floors of the giant impact basins of Hellas and Argyre."
Scientists have known for decades that winds change the surface of Mars, but Global Surveyor has also captured other dark streaks that scientists now believe are the result of recent landslides.
"This is the first time we have been able to detect from orbit a change caused by some other geologic process. Gravity is acting to move loose dust and sand down these crater slopes," said Edgett. "It's not a big surprise, but it is exciting to have captured the results of several new landslides that occurred in less than one Martian year." Mars Global Surveyor's camera is observing how often these streaks form, which will provide scientists with some idea of the rate at which Martian slopes are modified. "Knowing how long it takes for any process that changes the landscape to occur can tell us more about the how the planet came to look the way it does today," said Edgett.
The new images can be seen at:
Edgett and imaging team colleagues Dr. Michael Malin, also at Malin Space Science Systems, and Drs. Robert Sullivan, Peter Thomas and Joe Veverka of Cornell University, Ithaca, NY, are presenting these finding this week at the 31st Lunar and Planetary Science Conference, in Houston, TX.
Malin Space Science Systems built and operates the camera on board Mars Global Surveyor, which is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO, which developed and operates the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.
Univerity of Nevada, Reno
March 26, 1998
Mars' famous dust storms - which can be seen from backyard telescopes and sensationally cover the red planet's surface every several years - may be triggered by dust devils.
"Mars' atmosphere is extremely thin and very high wind velocities are needed to pick up dust. These dust devils, or mini-twisters, cause these high winds," said professor James R. Carr of the Department of Geological Sciences at the university's Mackay School of Mines.
Stephen Metzger, a doctoral student at Nevada, made the discovery from Mars Pathfinder imagery, using methods suggested by Carr. Metzger made the discovery in images downloaded from the NASA Jet Propulsion laboratory in Pasadena, Calif., using color filters.
By comparing and contrasting the Mars data with that from arid regions on Earth, such as Nevada, Metzger said much can be learned about local air pollution, acid rain and global climate change.
"Dust devils were thought to have been discovered by the Viking orbiter in 1976, but that was difficult to confirm," Carr said. "The significance of this discovery is that it confirms the Viking discovery and shows that dust devils are an important geological process on Mars. In fact, dust devils may be the primary soil erosion process on Mars."
Upon making the initial discovery, Metzger contacted Timothy Parker, a NASA scientist in Pasadena, and Jeff Johnson, U.S. Geological Survey scientist, in Flagstaff, Ariz., for verification and further image processing. Results of this image processing were presented Tuesday, March 17, in Houston at the Lunar and Planetary Science Conference.
After seeing these results at last week's international gathering of planetary scientists in Houston, several NASA science teams are eager to use the dust devil images in their atmospheric science and geology research, Metzger said.
NASA officials have credited Metzger and Carr as the first researchers to discover the dust devils in Pathfinder imagery. Metzger is a NASA Fellow, funded by the University of Nevada System Space Grant Consortium. He also is involved with the Desert Research Institute, a sister institution of the University of Nevada, Reno.
An image showing the dust devils is available.