Discovery of Buried Impact Craters on Mars Widens Possibility of an Ancient Martian Ocean

Soon after Mars was formed, it was bombarded by numerous large
meteorites and asteroids. Scientists have discovered an unexpectedly
large grouping of impact basins buried under Mars’ northern plains that
resulted from this pounding. They used Mars Orbiter Laser Altimeter
(MOLA) topographic data to find them, because they can’t be seen in
images of the Martian surface.

Above these basins are thin young plains, but the lowland crust beneath
them is actually extremely old and was formed very, very early.
According to Herbert Frey of the Geodynamics Branch of NASA’s Goddard
Space Flight Center, this is a radical departure from the popular
belief that the northern lowlands were formed later in Martian history,
perhaps by plate tectonic style processes.

Frey will discuss these findings on Thursday, November 8, at the
Geological Society of America’s annual meeting in Boston, Massachusetts.

This discovery is a crucial piece to one of the greatest unsolved puzzles
about Mars-why does its surface have two distinct hemispheres: one that
is high and heavily cratered and one that is low and sparsely cratered?
The origin of this fundamental “crustal dichotomy” is uncertain both
in terms of how and when it formed. But this recent discovery of the
numerous buried craters may pin down the answer to when the lowlands
first formed.

“The ancient age of the lowlands means whatever process produced them
occurred both early and relatively quickly,” explained Frey. “Things
like plate tectonics may not work. Another ramification is that there
have been lowlands in the northern parts of Mars for essentially all
of Martian history. That means that at whatever early time conditions
permitted liquid water to exist on Mars, there was a northern lowland
into which that water could drain. So it is quite possible that a
shallow ocean may have existed on Mars very early in its history, as
some have suggested based on completely different data.”

“The origin of the crustal dichotomy on Mars has been one of the main
areas of my own research for a long time, so anything that could tell
us how old the lowlands really were naturally was of interest,” Frey
said. “And of course, the discovery aspects of ‘seeing’ (in elevation
data) things that no one else had ever seen or even guessed might be
there is intrinsically intoxicating. Not only has this work turned out
to be very important, but it’s also been fun!”

CONTACT INFORMATION

During the GSA Annual Meeting, November 4-8, contact Ann Cairns or
Christa Stratton at the GSA Newsroom in the Hynes Convention Center,
Boston, Massachusetts, for assistance and to arrange for interviews:
(617) 954-3214.

The abstract for this presentation is available at:
http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_25358.htm

Post-meeting contact information:

Herbert Frey

Geodynamics Branch

Goddard Space Flight Center

Code 921

Greenbelt, MD 20771,

E-Mail: frey@core2.gsfc.nasa.gov

Phone: 301-614-6468

Fax: 301-614-6522

Ann Cairns

Director of Communications

Geological Society of America

Phone: 303-357-1056

Fax: 303-357-1074

E-mail: acairns@geosociety.org