http://www.asu.edu/news/stories/2007...711_themis.htm

ASU scientists keep an eye on Martian dust storm
Arizona State University
July 11, 2007

Scientists at ASU's Mars Space Flight Center are using the Thermal
Emission Imaging System (THEMIS) on NASA's Mars Odyssey orbiter to
monitor a large dust storm on the Red Planet.

The instrument, a multiwavelength camera sensitive to five visible
wavelengths and 10 infrared ones, is providing Mars scientists and
spacecraft controllers with global maps that track how much
atmospheric
dust is obscuring the planet.

Scientists at Arizona State University's Mars Space Flight Center are
using the Thermal Emission Imaging System (THEMIS) on NASA's Mars
Odyssey orbiter to monitor a large dust storm on the Red Planet. The
above image highlights the clouds of dust on the planet's surface.

The dust storm, which erupted during the last week of June, is
affecting
operations for all five spacecraft operating at Mars. The fleet
includes
two NASA rovers on the ground (Spirit and Opportunity), plus three
orbiters, two of which belong to NASA (Mars Odyssey and Mars
Reconnaissance Orbiter) and one to the European Space Agency (Mars
Express).

Beginning in Mars' heavily cratered southern highlands, the dust storm
took roughly a week to grow large enough to encircle the planet. Dust
has now drifted into the northern hemisphere as well.

"This is the favorable time of the Martian year for dust storms," says
Joshua Bandfield, research associate at the Mars Space Flight
Facility.

The facility is part of the School of Earth and Space Exploration in
ASU's College of Liberal Arts and Sciences.

"It's summer in the southern hemisphere," he says. "That's when Mars
lies closest to the sun and solar heating is greatest. We can watch
weather fronts spreading and kicking up dust in a big way."

Bandfield says that as winds sweep dust into the atmosphere, the
atmosphere becomes warmer. This adds to the storm's power, helping it
to
pick up more dust.

But the process has a built-in limitation, he says.

"When the dust becomes thick enough, it reflects more sunlight from
the
atmosphere, allowing the air near the surface to cool," Bandfield
says.

As seen from orbit, the dust storm has the effect of veiling surface
features - or even concealing them completely, which hasn't happened
yet
in this event.

"This storm isn't as big or severe as the one in 2001," Bandfield
says.
"THEMIS and other orbiters can still see the surface, despite the
continuing dust activity."

From the ground, the dust in the air has cut the amount of sunlight
reaching the rovers' solar panels, thus reducing their electrical
power.

"If you were standing there, you'd see the sky looking tawny with
haze,"
he says. "The sun would appear as a sharp-edged disk, but the light
level would be noticeably lower than what you would see under a
totally
clear sky."

Luckily, say scientists, summer is a time when the rovers can best
survive under reduced power. If the storm had struck during local
winter, the rovers might not get enough power during the day to stay
alive through the cold Martian night.

How long will this storm last? No one knows for sure, but Bandfield
notes its effects won't disappear as quickly as the storm erupted.

"Mars will remain dusty for at least a couple months more," he says.

Mars dust map images are available online at themis.asu.edu/dustmaps.
At
infrared wavelengths, the smallest details THEMIS can see on the
surface
are 330 feet (100 meters) wide. Philip Christensen, Regents' Professor
of geological sciences in ASU's School of Earth and Space Exploration,
is director of the Mars Space Flight Facility, as well as the designer
and principal investigator for the THEMIS instrument.

Robert Burnham,
(480) 458-8207