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Contact: Diane Ainsworth
FOR IMMEDIATE RELEASEMarch 13, 1998
NEW GLOBAL SURVEYOR DATA REVEAL DEEPLY LAYERED TERRAIN, MAGNETIC
FEATURES AND GENESIS OF A MARTIAN DUST STORM
For the first time in Mars exploration, a spacecraft has
captured the full evolution of a Martian dust storm. NASA's Mars
Global Surveyor mission also has returned new insights into the
deeply layered terrain and mineral composition of the Martian
surface, and to highly magnetized crustal features that provide
important clues about the planet's interior.
These findings are among the early results from the Mars-
orbiting mission being reported in today's issue of Science
This first set of formal results comes from data obtained in
October and November 1997, while the spacecraft was just
beginning to use the drag of Mars' upper atmosphere to lower and
circularize its orbit in a process called aerobraking. At the
time, a dust storm was brewing on Mars and had grown to about the
size of the South Atlantic Ocean.
The Global Surveyor data suggest that it began as a set of
small dust storms along the edge of the planet's southern polar
cap, according to Dr. Arden Albee of the California Institute of
Technology, Pasadena, CA, the Mars Global Surveyor mission
scientist. By Thanksgiving, it had expanded into a large regional
dust storm in Noachis Terra that covered almost 180 degrees
longitude, while spanning 20 degrees south latitude to nearly the
tip of the Martian equator.
"As this storm obscured the Martian landscape, we followed
it in detail using several instruments onboard Mars Global
Surveyor," Albee said. "The thermal emission spectrometer mapped
the temperature and opacity of the atmosphere while the camera
followed the visual effects. The effects of the storm extended
to great heights of about 130 kilometers (80 miles) and resulted
in great increases in both atmospheric density and variability
from orbit to orbit. These atmospheric measurements have great
significance for future Mars missions that will be using
aerobraking techniques too."
Before the storm, atmospheric dust was generally distributed
very uniformly, Albee said. Observations of the limb of the
planet in the northern hemisphere revealed both low-lying dust
hazes and detached water-ice clouds at altitudes of up to 55
kilometers (34 miles). Movement of these clouds was tracked by
the spectrometer as the planet rotated. Atmospheric turbulence
disrupted these cloud patterns as the small storms began to rise
and kick more dust into the air. As the storm began to abate,
small local storms began to crop up again along the edges of the
south polar cap, and ice clouds formed in depressions as the
carbon dioxide cap continued to retreat.
In addition to these unprecedented observations of a full-
blown Martian dust storm, measurements from the spacecraft's
magnetometer and electron reflectometer have yielded new findings
about Mars' strong, localized magnetic fields. These patches of
the crust, which register high levels of magnetism, are beginning
to unlock some of the mysteries surrounding Mars' internal dynamo
and when it died, said Dr. Mario Acuna of NASA's Goddard Space
Flight Center, Greenbelt, MD.
"These locally magnetized areas on Mars could not form
without the presence of an overall global magnetic field that was
perhaps as strong as Earth's is today," says Acuna. "Since the
internal dynamo that powered the global field is extinct, these
local magnetic fields act as fossils, preserving a record of the
geologic history and thermal evolution of Mars."
Magnetic fields are created by the movement of electrically
conducting fluids, and a planet can generate a global magnetic
field if its interior consists of molten metal hot enough to
undergo convective motion, similar to the churning motion seen in
"The small size and highly magnetic nature of these crustal
features, which measure on the order of 50 kilometers (30 miles),
are found within the ancient cratered terrain rather than within
the younger volcanic terrain," Acuna said. "By correlating
crustal age with magnetization, we have a perfect window on Mars'
past, which will help us to determine when Mars' internal dynamo
High-resolution images of dunes, sandsheets and drifts also
are helping reveal earlier chapters of Martian history. Landforms
shaped by erosion are almost everywhere, according to Albee, and
many bear a striking resemblance to Colorado's Rocky Mountains.
Rocky ridges poke through the Martian dust just as the jagged
edges of cliffs pierce through a blanket of snow in the Rockies.
Martian dust appears to have spilled down the sides of ridges
just as fresh snow slides down a ski slope.
"One almost expects to see ski tracks crisscrossing the
area," Albee added. "These images present a sharp contrast to the
images of boulder-strewn deserts found at the Viking and
Pathfinder landing sites."
Newly released images from the Mars Global Surveyor camera,
developed by principal investigator Dr. Michael Malin of Malin
Space Science Systems, Inc., San Diego, can be viewed on the
http://www.jpl.nasa.gov/marsnews/ or http://www.msss.com/
The Martian crust also exhibits much more layering at great
depth than was expected. The steep walls of canyons, valleys and
craters show the Martian crust to be stratified at scales of a
few tens of yards, which is an exciting discovery, Albee noted.
"At this point we simply do not know whether these layers
represent piles of volcanic flows or sedimentary rocks that might
have formed in a standing body of water," he said.
The thermal emission spectrometer, led by principal
investigator Dr. Philip Christensen of Arizona State University,
is beginning to obtain a few infrared emission spectra of the
surface, although it is still too cold on the surface for the
best results. The best spectra clearly indicate the presence of
pyroxene and plagioclase, minerals which are common in volcanic
rocks, with a variable amount of dust component. No evidence was
found for carbonate minerals, clay minerals or quartz. If
present in these rocks, their abundance must be less than about
Their absence indicates that carbonates are not ubiquitous
over the surface of the planet, but they may still be found in
specific locations that either favored their initial deposition
or their subsequent preservation. This finding could have
important implications for identifying areas that may preserve
signs of ancient life on Mars, since carbonate minerals are
commonly formed in biological processes, Albee said.
Striking results also have been obtained from Global
Surveyor's laser altimeter over Mars' northern hemisphere, which
is exceptionally flat with slopes and surface roughness
increasing toward the equator, according to principal
investigator Dr. David Smith of NASA Goddard Space Flight Center,
Greenbelt, MD. The initial data for this region helps scientists
interpret a variety of landforms, including the northern polar
cap, gigantic canyons, ridges, craters of all sizes and shield
volcanoes. Most surprising are views of extraordinarily mundane
regions -- as flat as the Bonneville Salt Flats in Utah - that
extend over vast northern regions of the planet.
Mars Global Surveyor will complete the first phase of its
two-part aerobraking strategy at the end of March, at which time
the science instruments will be turned on again for most of the
next six months. Over this period, the spacecraft will stay in an
11 1/2-hour orbit and collect an additional bounty of data at a
closest approach of about 170 kilometers (106 miles) above the
surface, much closer than the spacecraft will pass over the
planet once it has reached its formal mapping orbit in March
1999. This closer orbit will allow the science teams to take more
detailed measurements of the Martian atmosphere and surface
without magnetic interference from the solar wind.
"When we decided to slow the pace of aerobraking to reduce
the force on the solar panel that was damaged after launch, we
knew we would get a bonus - the ability to collect much more
science data closer to the planet than will be possible during
the prime mapping mission," said Glenn E. Cunningham, Mars Global
Surveyor project manager at NASA's Jet Propulsion Laboratory,
Pasadena, CA. "Additionally, the six-month period between the
end of March and early September will yield an extraordinary
opportunity as the lowest point of the orbit migrates over the
northern polar cap. All of this information that is coming back
now is really icing on the cake, a spectacular precursor to the
global mapping data expected to start flowing next year."
Mars Global Surveyor is part of a sustained program of Mars
exploration known as the Mars Surveyor Program. The mission 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, Pasadena, CA.