[meteorite-list] Surface Water May Have Existed Far Longer On Some Parts of Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 17 Sep 2008 10:15:19 -0700 (PDT)
Message-ID: <200809171715.KAA25886_at_zagami.jpl.nasa.gov>

September 16, 2008

Ed Stiles
Public Information Office
Planetary Science Institute
520-248-7119
psinews at psi.edu


SURFACE WATER MAY HAVE EXISTED FAR LONGER ON SOME PARTS OF MARS

Water may have played a role in shaping parts of the Martian landscape
a billion years longer than previous studies have shown, according to
a research team led by Catherine Weitz, a senior scientist with the
Planetary Science Institute.

Their research, to be published in "Geophysical Research Letters" and
now available online, presents strong evidence that sustained and
large-scale processes associated with precipitation and flowing water
likely occurred on the plains surrounding Valles Marineris during the
Hesperian Epoch, 3 to 3.7 billion years ago. Valles Marineris is a
huge canyon system that runs nearly a quarter of the way around the
planet at its equator.

According to many studies, runoff from precipitation ceased by the end
of the Noachian Epoch, which spanned the first billion years of
Martian history.

But after studying HiRISE images of light-toned layered deposits on
the plains surrounding Valles Marineris, Weitz and her co-authors
concluded that equatorial regions may have remained wet for a much
longer period.

Scientists have studied the light-toned layered deposits inside Valles
Marineris since the Mariner flybys in the early 1970s, but the HiRISE
camera flying aboard the Mars Reconnaissance Orbiter has now given
them an unparalleled, close-up view of the planet's features. HiRISE
can resolve objects as small as three feet in diameter.

Weitz was one of the first researchers to question whether the
light-toned layered deposits on the plains surrounding Valles
Marineris were different from those inside Valles Marineris. Two years
ago, she began aiming the HiRISE camera to photograph these layered
deposits.

"What we found was that these light-toned layered deposits on the
plains are very different from those within Valles Marineris," Weitz
said. "There are a lot of variations in brightness, color, and
erosional properties that we don't see for light-toned deposits inside
Valles Marineris. This suggests that the processes that created the
deposits outside Valles Marineris were different from those operating
inside."

Weitz found light-toned layered deposits associated with valley
systems and inverted channels in two locations near Valles Marineris.
Inverted channels form on Earth when sediment is deposited in
streambeds over time. When the streams dry up, the surrounding, softer
terrain erodes away, leaving the harder, cemented sediments in the
former streambeds standing above the surrounding terrain.

Weitz and her colleagues also have found valley systems that probably
were created by running water in two other areas of light-toned
layered deposits adjacent to Valles Marineris.

All of these phenomena point toward what geologists call fluvial
processes ? those associated with running water.

In addition, the CRISM spectrometer. which is also on the Mars
Reconnaissance Orbiter, identified minerals in the light-toned layered
deposits that often form in the presence of liquid water on Earth.

However, other explanations for the layered deposits and mineralogy
cannot be ruled out, Weitz said. These could involve explosive
volcanism, wind deposition, and other geological processes.

"But the fact that these deposits are so distinct from other
light-toned layered deposits in their characteristics and in their
association with valleys and inverted channels suggests a fluvial
origin," she said.

"This was a big surprise because no one thought we'd be seeing these
extensive fluvial systems in the plains all around Valles Marineris
that were formed during the Hesperian Era," Weitz said. "Everyone
thought that by then the climate had pretty much dried out."

"What we're seeing tells us that this light-toned layering on the
plains was associated with fluvial activity that wasn't occurring just
in little pockets over very brief episodes, but rather on a much
larger scale for sustained time periods," she added. "For some reason,
there was precipitation around Valles Marineris that allowed these
systems to form out on the plains."

Others involved in the research include Ralph Milliken, of the Jet
Propulsion Laboratory; John Grant, of the Smithsonian Institution's
Air and Space Museum; Alfred McEwen, of the Lunar and Planetary Lab at
The University of Arizona; Rebecca Williams, of the Planetary Science
Institute; and Janice Bishop, of the SETI Institute.

The article can be accessed at
http://www.agu.org/journals/pip/gl/2008GL035317-pip.pdf

CONTACT:
Cathy Weitz
1-520-622-6300
weitz at psi.edu

PSI Information:
Mark V. Sykes, Director
1-520-622-6300
sykes at psi.edu

PSI Homepage http://www.psi.edu
Received on Wed 17 Sep 2008 01:15:19 PM PDT