NASA’s Mars Global Surveyor Captures Dust Storms

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Daily global maps, created with images from NASA’s Mars
Global Surveyor spacecraft, provide a moving picture of
Martian weather during 1999-2000 similar to the familiar
satellite weather maps we see of Earth.

The Martian weather maps will be presented today at the
American Geophysical Union meeting in Boston by Dr. Andrew
Ingersoll, professor of planetary science at the California
Institute of Technology, Pasadena, and an interdisciplinary
scientist with Mars Global Surveyor and member of the imaging
team.

In one day, Global Surveyor’s camera covers the planet in
12 or 13 overlapping colored strips, which scientists seamed
together to make a global movie. Scientists use these movies
to study the advance and retreat of the polar frost as well as
the motion of dust storms and ice clouds to understand the
changing weather on Mars.

“Dust plays the same role in Martian weather that water
plays on Earth,” Ingersoll said. “Dust heats the atmosphere by
absorbing sunlight and starts small storms that every few
years merge into major weather events. Some years are dusty
and some are not. We blame our wet and dry years on El Nino,
but no such scapegoat exists for Mars. That is the mystery.
Without oceans or another large heat reservoir that sloshes
back and forth, every year on Mars should be the same as every
other.”

The Martian year just past, which started when Mars
Global Surveyor entered its mapping orbit in March 1999, was a
low dust year. Countless dust devils and hundreds of local
dust storms scoured the surface but only a few grew to
regional scale, and none made it into the global category. In
contrast, the Viking landers experienced two great global dust
storms the year after they touched down in 1976, Ingersoll
explained. “The Global Surveyor movies are better than
anything Viking could have produced. A second or third year of
data would allow us to document this mysterious interannual
variability and understand why global dust storms are so
unpredictable.”

As during the Viking era, most of the dust storms
occurred when Mars was closest to the Sun, which happens
during the northern fall season. The largest storms started in
the north and spread across the equator at speeds up to about
32 kilometers per hour (20 mph). During the Viking years the
large dust storms started in the south, where it was
springtime. Also, more storms started near the edge of the
polar caps than during the Viking era.

“Apparently, Mars is poised at a critical point where
natural fluctuations in the daily weather are just barely able
to trigger a global dust storm,” Ingersoll said. “It is
unlikely that Mars was put together in such an unstable state.
More likely, it maintains itself there. One way is if the
supply of dust is limited. It gets scoured away by the global
winds and hides behind boulders and other obstacles. Gradually
the dust devils and local storms bring it out into the open,
at which point the planet is poised again for another global
dust storm.”

For more information, go to http://mars.jpl.nasa.gov/mgs

Mars Global Surveyor is managed by the Jet Propulsion
Laboratory for NASA’s Office of Space Science, Washington,
D.C. JPL is a division of the California Institute of
Technology in Pasadena.