Layers Piled in a Mars Crater Record a History of Changes

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

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

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

NEWS RELEASE: 2010-044 Feb. 11, 2010

LAYERS PILED IN A MARS CRATER RECORD A HISTORY OF CHANGES

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-044&cid=release_2010-044

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.

-end

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