Mars Rover Examines Odd Material at Small, Young Crater

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

NEWS RELEASE: 2010-096 March 24, 2010

Mars Rover Examines Odd Material at Small, Young Crater

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-096&cid=release_2010-096


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 "Concepción" 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
Concepción is at http://photojournal.jpl.nasa.gov/catalog/PIA12969 .

The rocks ejected outward from the impact that dug Concepción 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 Concepción 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 Concepción 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 Concepción 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 Concepción 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 .

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