(Thanks to Ron Baalke)

Nancy Neal-Jones / Cynthia O'Carroll October 17, 2005
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-0039 / 4647)

Release: 05-46

NEW MAP PROVIDES MORE EVIDENCE MARS ONCE LIKE EARTH

NASA scientists have discovered additional evidence that Mars once
underwent plate tectonics, slow movement of the planet's crust, like the
present-day Earth. A new map of Mars' magnetic field made by the Mars
Global Surveyor spacecraft reveals a world whose history was shaped by
great crustal plates being pulled apart or smashed together.

Scientists first found evidence of plate tectonics on Mars in 1999. Those
initial observations, also done with the Mars Global Surveyor's
magnetometer, covered only one region in the Southern Hemisphere. The data
was taken while the spacecraft performed an aerobraking maneuver, and so
came from differing heights above the crust.

This high resolution magnetic field map, the first of its kind, covers the
entire surface of Mars. The new map is based on four years of data taken in
a constant orbit. Each region on the surface has been sampled many times.
"The more measurements we obtain, the more accuracy, and spatial
resolution, we achieve," said Dr. Jack Connerney, co-investigator for the
Mars Global Surveyor magnetic filed investigation at NASA's Goddard Space
Flight Center, Greenbelt, Md.

"This map lends support to and expands on the 1999 results," said Dr.
Norman Ness of the Bartol Research Institute at the University of Delaware,
Newark. "Where the earlier data showed a 'striping' of the magnetic field
in one region, the new map finds striping elsewhere. More importantly, the
new map shows evidence of features, transform faults, that are a
'tell-tale' of plate tectonics on Earth." Each stripe represents a magnetic
field pointed in one direction - positive or negative - and the alternating
stripes indicate a "flipping" of the direction of the magnetic field from
one stripe to another.

Scientists see similar stripes in the crustal magnetic field on Earth.
Stripes form whenever two plates are being pushed apart by molten rock
coming up from the mantle, such as along the Mid-Atlantic Ridge. As the
plate spreads and cools, it becomes magnetized in the direction of the
Earth's strong global field. Since Earth's global field changes direction
a few times every million years, on average, a flow that cools in one
period will be magnetized in a different direction than a later flow. As
the new crust is pushed out and away from the ridge, stripes of alternating
magnetic fields aligned with the ridge axis develop. Transform faults,
identified by "shifts" in the magnetic pattern, occur only in association
with spreading centers.

To see this characteristic magnetic imprint on Mars indicates that it, too,
had regions where new crust came up from the mantle and spread out across
the surface. And when you have new crust coming up, you need old crust
plunging back down - the exact mechanism for plate tectonics.

Connerney points out that plate tectonics provides a unifying framework to
explain several Martian features. First, there is the magnetic pattern
itself. Second, the Tharsis volcanoes lie along a straight line. These
formations could have formed from the motion of a crustal plate over a
fixed "hotspot" in the mantle below, just as the Hawaiian islands on Earth
are thought to have formed. Third, the Valles Marineris, a large canyon
six times as long as the Grand Canyon and eight times as deep, looks just
like a rift formed on Earth by a plate being pulled apart. Even more, it
is oriented just as one would expect from plate motions implied by the
magnetic map.

"It's certainly not an exhaustive geologic analysis," said Dr. Mario Acuña,
principal investigator for the Mars Global Surveyor magnetic filed
investigation at Goddard Space Flight Center. "But plate tectonics does
give us a consistent explanation of some of the most prominent features on
Mars."

Results were published in the Oct. 10 edition of the Proceedings of the
National Academy of Science.

Other scientists working on the project included Dr. G. Kletetschka of the
Catholic University of America, Washington, DC, and Goddard Space Flight
Center; Dr. D.L. Mitchell and Dr. R.P. Lin of the University of California
at Berkeley; and Dr. H. Reme of the Centre d’Etude Spatiale des
Rayonnements in France. Dr. Acuña leads the international team that built
and operates the Mars Global Surveyor magnetometers. The Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, manages the mission for NASA's Science Mission Directorate in
Washington.

For more information on the results, consult: http://www.nasa.gov/vision/universe/solarsystem/mgs_plates.html