[meteorite-list] Mars Rover Examines Odd Material at Small, Young Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 25 Mar 2010 16:29:51 -0700 (PDT)
Message-ID: <201003252329.o2PNTqST011871_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-096

Mars Rover Examines Odd Material at Small, Young Crater
Jet Propulsion Laboratory
March 24, 2010

PASADENA, Calif -- Weird coatings on rocks beside a young Martian crater
remain puzzling after a preliminary look at data from examination of the
site by NASA's Opportunity rover.

The rover spent six weeks investigating the crater called "Concepci??n"
before resuming its long journey this month. The crater is about 10
meters (33 feet) in diameter. Dark rays extending from it, as seen from
orbit, flagged it in advance as a target of interest because the rays
suggest the crater is young. An image from orbit showing Opportunity
beside Concepci??n is at http://photojournal.jpl.nasa.gov/catalog/PIA12969 .

The rocks ejected outward from the impact that dug Concepci??n are chunks
of the same type of bedrock Opportunity has seen at hundreds of
locations since landing in January 2004: soft, sulfate-rich sandstone
holding harder peppercorn-size dark spheres like berries in a muffin.
The little spheres, rich in iron, gained the nickname "blueberries."

"It was clear from the images that Opportunity took on the approach to
Concepci??n that there was strange stuff on lots of the rocks near the
crater," said Steve Squyres of Cornell University, Ithaca, N.Y.,
principal investigator for Opportunity and its twin rover, Spirit.
"There's dark, grayish material coating faces of the rocks and filling
fractures in them. At least part of it is composed of blueberries jammed
together as close as you could pack them. We've never seen anything like
this before."

Opportunity used tools on its robotic arm to examine this unusual
material on a rock called "Chocolate Hills." In some places, the layer
of closely packed spheres lies between thinner, smoother layers. "It
looks like a blueberry sandwich," said Matt Golombek, a rover
science-team member at NASA's Jet Propulsion Laboratory, Pasadena,
Calif. An image of the coating material is at
http://photojournal.jpl.nasa.gov/catalog/PIA12970 .

Initial analysis of the coating's composition does not show any obvious
component from whatever space rock hit Mars to dig the crater, but that
is not a surprise, Golombek said. "The impact is so fast, most of the
impactor vaporizes," he said. "Thin films of melt get thrown out, but
typically the composition of the melt is the stuff that the impactor
hit, rather than the impactor material."

The composition Opportunity found for the dark coating material fits at
least two hypotheses being evaluated, and possibly others. One is that
the material resulted from partial melting of blueberry-containing
sandstone from the energy of the impact. Another is that it formed from
filling of fractures in this type of rock before the impact occurred.

"It's possible that when you melt this rock, the sandstone melts before
the blueberries do, leaving intact blueberries as part of a melt layer,"
Squyres said. "As an alternative, we know that this type of rock has
fractures and that the sandstone can dissolve. Long ago, water flowing
through fractures could have dissolved the sandstone and liberated
blueberries that fell down into the fracture and packed together. In
this hypothesis, the impact that excavated the crater did not play a
role in forming this material, but split rocks along fractures so the
material is exposed on the exterior like a coating."

Golombek said, "One consideration that jumps out is that we've been
driving around this part of Mars for six years and never seen this stuff
before, then we get to this young crater and it's coating rocks all
around the crater. Sure looks like there's a connection, but it could
just be a coincidence."

The observation that the rocks thrown from the crater have not yet
eroded away much is evidence that the crater is young, confirming the
suggestion from the dark rays. Squyres said, "We're not ready to attach
a number to it, but this is really young. It is the youngest crater
we've ever seen with Opportunity and probably the youngest either rover
has seen."

One question Opportunity's visit did answer was about the dark rays: "We
wondered before getting to Concepci??n why the rays are dark," Golombek
said. "We found out that the rays are areas with blocks of light-toned
sandstone ejected from the crater. They look dark from orbit because of
the shadows that the blocks are casting when the orbital images are
taken in mid-afternoon."

Since departing Concepci??n on March 9, Opportunity has driven 614 meters
(2,014 feet) farther along the route to its long-term destination at
Endeavour Crater, about 19 kilometers (12 miles) in diameter and still
at a drive distance of more than 12 kilometers (7 miles).

Squyres said, "We're on the road again. We have a healthy rover and we
have enough power for substantial drives. We want to get to Endeavour
with a healthy rover. It takes a compelling target for us to stop and
study. And Concepci??n was a compelling target." JPL, a division of the
California Institute of Technology in Pasadena, manages the Mars
Exploration Rover Project for the NASA Science Mission Directorate,
Washington. For more information about the Mars rovers, visit
http://www.nasa.gov/rovers .

> View all related images
<http://www.jpl.nasa.gov/news/features.cfm?feature=2529>

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

2010-096
Received on Thu 25 Mar 2010 07:29:51 PM PDT