[meteorite-list] Layers in a Mars Crater Record a History of Changes

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 11 Feb 2010 14:26:11 -0800 (PST)
Message-ID: <201002112226.o1BMQBc3016810_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-044

Layers in a Mars Crater Record a History of Changes
Jet Propulsion Laboratory
February 11, 2010

PASADENA, Calif. -- Near the center of a Martian crater about the size
of Connecticut, hundreds of exposed rock layers form a mound as tall as
the Rockies and reveal a record of major environmental changes on Mars
billions of years ago.

The history told by this tall parfait of layers inside Gale Crater
matches what has been proposed in recent years as the dominant
planet-wide pattern for early Mars, according to a new report by
geologists using instruments on NASA's Mars Reconnaissance Orbiter.

"Looking at the layers from the bottom to the top, from the oldest to
the youngest, you see a sequence of changing rocks that resulted from
changes in environmental conditions through time," said Ralph Milliken
of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This thick
sequence of rocks appears to be showing different steps in the
drying-out of Mars."

Using geological layers to understand stages in the evolution of a
planet's climate has a precedent on Earth. A change about 1.8 billion
years ago in the types of rock layers formed on Earth became a key to
understanding a dramatic change in Earth's ancient atmosphere.

Milliken and two co-authors report in Geophysical Research Letters that
clay minerals, which form under very wet conditions, are concentrated in
layers near the bottom of the Gale stack. Above that, sulfate minerals
are intermixed with the clays. Sulfates form in wet conditions and can
be deposited when the water in which they are dissolved evaporates.
Higher still are sulfate-containing layers without detectable clays. And
at the top is a thick formation of regularly spaced layers bearing no
detectable water-related minerals.

Rock exposures with compositions like various layers of the Gale stack
have been mapped elsewhere on Mars, and researchers, including
Jean-Pierre Bibring of the University of Paris, have proposed a Martian
planetary chronology of clay-producing conditions followed by
sulfate-producing conditions followed by dry conditions. However, Gale
is the first location where a single series of layers has been found to
contain these clues in a clearly defined sequence from older rocks to
younger rocks.

"If you could stand there, you would see this beautiful formation of
Martian sediments laid down in the past, a stratigraphic section that's
more than twice the height of the Grand Canyon, though not as steep,"
said Bradley Thomson of the Johns Hopkins University Applied Physics
Laboratory, Laurel, Md. He and John Grotzinger of the California
Institute of Technology in Pasadena are Milliken's co-authors.

NASA selected Gale Crater in 2008 as one of four finalist sites for the
Mars Science Laboratory rover, Curiosity, which has a planned launch in
2011. The finalist sites all have exposures of water-related minerals,
and each has attributes that distinguish it from the others. This new
report is an example of how observations made for evaluating the
landing-site candidates are providing valuable science results even
before the rover mission launches.

Three instruments on NASA's Mars Reconnaissance Orbiter have provided
key data about the layered mound in Gale Crater. Images from the High
Resolution Imaging Science Experiment camera reveal details used to map
hundreds of layers. Using stereo pairs of the images, the U.S.
Geological Survey has generated three-dimensional models used to discern
elevation differences as small as a meter (about a yard). Observations
by the Compact Reconnaissance Imaging Spectrometer for Mars yielded
information about minerals on the surface. The Context Camera provided
broader-scale images showing how the layers fit geologically into their
surroundings.

Thomson said, "This work demonstrates the synergy of the instruments on
the Mars Reconnaissance Orbiter. We wouldn't have as complete a picture
if we were missing any of the components."

The mission has been studying Mars since 2006. It has returned more data
from the planet than all other Mars missions combined. More information
about this mission is at http://www.nasa.gov/mro.

Malin Space Science Systems, San Diego, provided and operates the
Context Camera. Johns Hopkins University Applied Physics Laboratory
provided and operates the Compact Reconnaissance Imaging Spectrometer.
The University of Arizona Lunar and Planetary Laboratory, Tucson,
operates the High Resolution Imaging Science Experiment, which was built
by Ball Aerospace & Technologies Corp., Boulder, Colo.

JPL, a division of Caltech, manages the Mars Reconnaissance Orbiter for
NASA's Science Mission Directorate, Washington. Lockheed Martin Space
Systems, Denver, is the prime contractor for the project and built the
spacecraft.

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

Michael Buckley 240-228-7536
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
michael.buckley at jhuapl.edu

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

2010-044
Received on Thu 11 Feb 2010 05:26:11 PM PST