[meteorite-list] Pebbly Rocks Testify to Old Streambed on Mars (MSL)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 30 May 2013 12:01:25 -0700 (PDT)
Message-ID: <201305301901.r4UJ1PRY022541_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-181

Pebbly Rocks Testify to Old Streambed on Mars
Jet Propulsion Laboratory
May 30, 2013

PASADENA, Calif. - Detailed analysis and review have borne out
researchers' initial interpretation of pebble-containing slabs that
NASA's Mars rover Curiosity investigated last year: They are part of an
ancient streambed.

The rocks are the first ever found on Mars that contain streambed
gravels. The sizes and shapes of the gravels embedded in these
conglomerate rocks -- from the size of sand particles to the size of
golf balls -- enabled researchers to calculate the depth and speed of
the water that once flowed at this location.

"We completed more rigorous quantification of the outcrops to
characterize the size distribution and roundness of the pebbles and sand
that make up these conglomerates," said Rebecca Williams of the
Planetary Science Institute, Tucson, Ariz., lead author of a report
about them in the journal Science this week. "We ended up with a
calculation in the same range as our initial estimate last fall. At a
minimum, the stream was flowing at a speed equivalent to a walking pace
-- a meter, or three feet, per second -- and it was ankle-deep to
hip-deep."

Three pavement-like rocks examined with the telephoto capability of
Curiosity's Mast Camera (Mastcam) during the rover's first 40 days on
Mars are the basis for the new report. One, "Goulburn," is immediately
adjacent to the rover's "Bradbury Landing" touchdown site. The other
two, "Link" and "Hottah," are about 165 and 330 feet (50 and 100 meters)
to the southeast. Researchers also used the rover's laser-shooting
Chemistry and Camera (ChemCam) instrument to investigate the Link rock.

"These conglomerates look amazingly like streambed deposits on Earth,"
Williams said. "Most people are familiar with rounded river pebbles.
Maybe you've picked up a smoothed, round rock to skip across the water.
Seeing something so familiar on another world is exciting and also
gratifying."

The larger pebbles are not distributed evenly in the conglomerate rocks.
In Hottah, researchers detected alternating pebble-rich layers and sand
layers. This is common in streambed deposits on Earth and provides
additional evidence for stream flow on Mars. In addition, many of the
pebbles are touching each other, a sign that they rolled along the bed
of a stream.

"Our analysis of the amount of rounding of the pebbles provided further
information," said Sanjeev Gupta of Imperial College, London, a
co-author of the new report. "The rounding indicates sustained flow. It
occurs as pebbles hit each other multiple times. This wasn't a one-off
flow. It was sustained, certainly more than weeks or months, though we
can't say exactly how long."

The stream carried the gravels at least a few miles, or kilometers, the
researchers estimated.

The atmosphere of modern Mars is too thin to make a sustained stream
flow of water possible, though the planet holds large quantities of
water ice. Several types of evidence have indicated that ancient Mars
had diverse environments with liquid water. However, none but these
rocks found by Curiosity could provide the type of stream flow
information published this week. Curiosity's images of conglomerate
rocks indicate that atmospheric conditions at Gale Crater once enabled
the flow of liquid water on the Martian surface.

During a two-year prime mission, researchers are using Curiosity's 10
science instruments to assess the environmental history in Gale Crater
on Mars, where the rover has found evidence of ancient environmental
conditions favorable for microbial life.

More information about Curiosity is online at:
http://www.jpl.nasa.gov/msl , http://www.nasa.gov/msl and
http://mars.jpl.nasa.gov/msl/ .

You can follow the mission on Facebook at:
http://www.facebook.com/marscuriosity and on Twitter at
http://www.twitter.com/marscuriosity .

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

2013-181
Received on Thu 30 May 2013 03:01:25 PM PDT