The largest dust storm to be seen on Mars since NASA’s
Mars Global Surveyor spacecraft arrived in 1997 is currently
raging across about half the planet.

“This is by far the largest storm we’ve seen during the
Mars Global Surveyor mission,” said Dr. Philip Christensen of
Arizona State University in Tempe, principal investigator for
the Global Surveyor’s thermal emission spectrometer. The
instrument has been monitoring the Martian atmosphere since
March 1999. “We expect that the storm will continue to grow –
– perhaps becoming a global storm of the type that was seen
during the Mariner 9 and Viking missions in the 1970s,”
Christensen said.

Daily observations by the instrument are made into maps
that allow scientists to determine both the temperature and
the amount of dust in the atmosphere. Mars dust storm maps
are posted at .

Scientists first noticed the onset of the storm June 15,
2001 when a region of dust began to appear in the Hellas Basin
in the southern hemisphere. A week and a half later, on June
26, the storm began to intensify and expand. Since then, the
storm has dramatically grown in size and severity. The dust
storm has expanded well into the northern hemisphere and has
wrapped more than halfway around the planet, Christensen said.
This storm also began earlier than normal for Martian dust
storms. In the past when a large storm has occurred early in
the season, there are usually several large storms during the
year. NASA scientists will be monitoring Mars over the next
few months to see how this major storm develops and to test
their predictions of more storms to come.

The storm should not have a major impact on the planned
arrival of another spacecraft, the 2001 Mars Odyssey, in
October, Christensen said. Odyssey will use repeated passes
through Mars’ upper atmosphere to slow the spacecraft and
lower its orbit around the red planet. “We’ll use the
instruments on Global Surveyor to monitor the atmosphere on an
hourly basis, providing the Odyssey spacecraft team the
information they need to keep Odyssey at the proper height
where it can safely fly through the atmosphere,” Christensen
said. Odyssey’s orbit height can be adjusted as needed in
response to the changing atmosphere as observed by Global
Surveyor, he said.

For more information on the Mars Exploration Program, see .

Global Surveyor was launched in November 1996, and Mars
Odyssey was launched in April 2001. Both missions are managed
by JPL for NASA’s Office of Space Science, Washington, D.C.
Lockheed Martin Astronautics, Denver, Colo., developed and
operates both spacecraft. The thermal emission spectrometers
on each spacecraft are operated by Arizona State University.
JPL is a division of the California Institute of Technology in