MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Franklin O'Donnell
FOR IMMEDIATE RELEASE
August 10, 1999
SHARPEST-EVER MARS IMAGES REVEAL ACTIVE RED PLANET
Newly released images from NASA's Mars Global Surveyor show
that the red planet is a different place today than it was two
years ago when the spacecraft arrived -- a world constantly
reshaped by forces of nature including shifting sand dunes,
monster dust devils, wind storms, frosts and polar ice caps that
grow and retreat with the seasons.
"Mars is a cold, dry desert, but our camera has shown it is
far from being a stagnant place," said Dr. Michael Malin,
principal investigator for the Mars Global Surveyor camera at
Malin Space Science Systems, San Diego, CA. "Over the past few
months, we have captured a unique record of seasonal and
meteorological events, which demonstrates that Mars is active
and dynamic today."
The spacecraft's camera monitors the planet's weather on a
daily basis from orbit, just like weather satellites on Earth.
Today, Mars is a much more dynamic place than the planet the
Viking orbiters and landers saw in the late 1970s. The weather
has been particularly active during the past two months, as
spring arrived in the southern hemisphere and autumn approached
in the north.
"Storm clouds have been brewing over the north polar ice
cap all through the month of July, and soon, ever-increasing
portions of the north polar cap will be plunged into wintertime
darkness," Malin said. "As the season changes rapidly, clouds
will cover much of the northern plains and it might begin to
snow as the polar cap expands."
In other regions of Mars, dust devils are the prevailing
weather story. Dust devils result from spinning vortices of air
that arise when the ground is heated and general wind flow is
light. On Earth they are relatively small features, but on
Mars, dust devils are thought by some to be a major transporter
of the fine, pinkish dust that gives the sky its unearthly
brownish color, as seen by the Mars Pathfinder and Viking
landers. Dust devils may also help initiate the seasonal
raising of dust over wide areas of Mars.
In mid-May, swirling columns of dust as high as five miles
(eight kilometers) were observed in northern Amazonis Planitia.
Dust devils in this area, northwest of the large Tharsis
volcanoes, appear to be common; they were also seen by the
Viking missions of the 1970s. The average dust devil is slow-
moving and may carry several tons of dust within its height of
1.2 miles (two kilometers).
Each lasts for a few hours at most during the hottest part
of the Martian day in the late afternoon, Malin said. Although
the winds in these vortices are sufficient to raise dust, they
have much less power than tornadoes on Earth, which develop
under very different meteorological circumstances.
Global Surveyor's camera has also returned tantalizing
evidence of recent shifting sands in dune fields first seen in
Mariner 9 pictures of Mars from the early 1970s. Scientists are
interested in dune fields isolated within large impact craters
because their dark color suggests that the dust which covers
much of the rest of the planet does not accumulate on their
"This indicates that the dunes must be moving and that over
time we may be able to see changes that will allow us to measure
the rates of wind erosion on Mars," Malin explained.
Sand dunes also are giving Mars scientists some new
insights as to how Mars' seasonal polar ice caps retreat at the
end of each winter as seasonal warming occurs. The most
dramatic views show patches of dark sand poking through fields
of carbon dioxide frost. First seen in 1998 in the north polar
region, the same features have been seen this year on dunes near
the south pole.
"These pictures look like aerial photographs of dunes on
Earth," Malin said. "They are so unusual in this context that
we thought for a while that we were looking at a process that
involves small 'explosions,' but the new images showed that wind
was responsible for the streaks we were seeing." The dark spots
on frost-covered dunes continue to grow and spread as spring
approaches until, eventually, the entire dune field is frost-
A variety of new images of Mars is available on the
Mars Global Surveyor is the first mission in a long-term
program of Mars exploration, known as the Mars Surveyor Program,
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, Pasadena, CA.