Contact: Mary Hardin

New images from NASA’s Mars Global Surveyor spacecraft have
caught dust devils and landslides in the act of changing the
surface of Mars, giving scientists more clues about how Mother
Nature’s vandals are leaving their mark on the changing Martian

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

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

“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 and

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.