[meteorite-list] Mars Reconnaissance Orbiter Provides Insights About Mars Water and Climate

[Ron Baalke]

Sept. 20, 2007

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

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

Lori Stiles
University of Arizona, Tucson
520-626-4402
lstiles at email.arizona.edu

RELEASE: 07-206

NASA ORBITER PROVIDES INSIGHTS ABOUT MARS WATER AND CLIMATE

PASADENA, Calif. -- NASA's Mars Reconnaissance Orbiter (MRO) is 
examining several features on Mars that address the role of water at 
different times in Martian history. 

Features examined with the orbiter's advanced instruments include 
material deposited in two gullies within the past eight years, polar 
ice layers formed in the recent geologic past, and signs of water 
released by large impacts when Mars was older.

Last year, discovery of the fresh gully deposits from before-and-after 
images taken since 1999 by another orbiter, Mars Global Surveyor, 
raised hopes that modern flows of liquid water had been detected on 
Mars. Observations by the newer orbiter, which reached Mars last 
year, suggest these deposits might instead have resulted from 
landslides of loose, dry materials. Researchers report this and other 
findings from the MRO in five papers in Friday's issue of the journal 
Science.

"The key question raised by these two deposits is whether water is 
coming to the surface of Mars today." said Alfred McEwen of the 
University of Arizona, Tucson, lead scientist for the spacecraft's 
High Resolution Imaging Science Experiment camera and co-author of 
three of the papers. "Our evidence suggests the new deposits did not 
necessarily involve water."

One of the fresh deposits is a stripe of relatively bright material 
several hundred yards long that was not present in 1999 but appeared 
by 2004. The orbiter's Compact Reconnaissance Infrared Spectrometer 
for Mars reveals the deposit is not frost, ice or a mineral left 
behind by evaporation of salty water. Also, the researchers inspected 
the slopes above this and five other locations that have bright and 
apparently young deposits. The slopes are steep enough for sand or 
loose, dry dust to flow down the gullies. Bright material seen uphill 
could be the source.

Other gullies, however, offer strong evidence of liquid water flowing 
on Mars within the last few million years, although perhaps at a 
different phase of repeating climate cycles. Mars, like Earth, has 
periodic changes in climate due to the cycles related to the planets' 
tilts and orbits. Some eras during the cycles are warmer than others. 
These gullies are on slopes too shallow for dry flows, and images 
from MRO's high-resolution camera show clear indicators of liquid 
flows, such as braided channels and terraces within the gullies. 

Another new finding from that camera may help undermine arguments that 
very ancient Mars had a wet climate on a sustained basis. Landscapes 
with branched channels and fan-like deposits typical of liquid flows 
were found around several impact craters. Images show close 
association between some of those flow features and ponded deposits 
interpreted as material melted by the impact of a meteoroid into 
ice-rich crust. This new evidence supports a hypothesis that ancient 
water flows on the surface were episodic, linked to impact events and 
subsurface heating, and not necessarily the result of precipitation 
in a sustained warmer climate. Crater-digging impacts were larger and 
more numerous during the early Martian era when large drainage 
networks and other signs of surface water were carved on many parts 
of the planet.

The MRO has examined ice-rich layered deposits near the Martian poles 
with the ground-penetrating Shallow Subsurface Radar instrument, and 
other experiments. The radar detected layering patterns near the 
south pole that suggest climatic periods of accumulating deposits 
have alternated with periods of erosion, report Roberto Seu of the 
University of Rome and co-authors. Maria Zuber of the Massachusetts 
Institute of Technology, and collaborators used effects of Mars' 
gravity on the orbiter to check whether layered deposits at the south 
pole are high-density material, such as rock, or lower-density such 
as ice. Their observations add to other evidence that the layers are 
mostly water. Kenneth Herkenhoff of the U.S. Geological Survey, 
Flagstaff, and others used the high-resolution camera to trace a 
series of distinctive layers near the north pole.

An accompanying paper by Windy Jaeger of the U.S. Geological Survey, 
Flagstaff, and co-authors uses images from the high-resolution camera 
to show lava flows completely draping a young Martian channel network 
called Athabasca Valles This creates ponded lava over an expanse that 
other researchers had interpreted in 2005 as a frozen sea.

Richard Zurek, project scientist for MRO at NASA's Jet Propulsion 
Laboratory (JPL), Pasadena, Calif., said, "These latest increases in 
observational capabilities, individually and in combination, reveal a 
more complex Mars, a planet with a rich history that we are still 
learning to read."

JPL manages the MRO mission for NASAs Science Mission Directorate, 
Washington. Lockheed Martin Space Systems, Denver, is the prime 
contractor and built the spacecraft. The University of Arizona 
operates the High Resolution Imaging Science Experiment camera, built 
by Ball Aerospace & Technology Corp., Boulder, Colo. The Johns 
Hopkins University Applied Physics Laboratory, Laurel, Md., operates 
the Compact Reconnaissance Imaging Spectrometer for Mars. The Shallow 
Subsurface Radar was provided by the Italian Space Agency; its 
operations are led by the University of Rome, and its data analyzed 
by a joint Italian-U.S. science team. 

Images from the new reports are available online at:

http://www.nasa.gov/mission_pages/MRO/multimedia/20070920.html 

Additional information about NASA's Mars Reconnaissance Orbiter is 
online at:

http://www.nasa.gov/mro

	
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