NASA’s Mars Exploration Rover Opportunity has begun sampling rocks
blasted out from a stadium-sized impact crater the rover is circling,
and the very first one may extend our understanding about the region’s
wet past.
Opportunity is spending a few weeks examining the crater, informally
named “Endurance,” from the rim, providing information NASA will use
for a decision about whether to send the rover down inside. That
decision will take into account both the scientific allure of rock
layers in the crater and the operational safety of the rover.
Opportunity has completed observations from the first of three planned
viewpoints located about one-third of the way around the rim from each
other. Mission controllers at NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., are sending the rover around the crater’s rim
counterclockwise.
“As we were proceeding from our first viewpoint toward our second
viewpoint, we saw a rock that looked like nothing we’d ever seen
before,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y.,
principal investigator for the science instruments on both Mars
Exploration Rovers. The rock appears to have come from below the
area’s current surface level, tossed up by the impact that excavated
Endurance Crater.
This rock, dubbed “Lion Stone,” is about 10 centimeters tall and 30
centimeters long (4 inches by 12 inches). In some ways it resembles
rocks that provided evidence of past water at the smaller crater,
“Eagle Crater,” in which Opportunity landed. Like them, it has a
sulfur-rich composition, fine layering and spherical concretions, and
likely formed under wet conditions.
“However,” Squyres said, “it is different in subtle ways from what we
saw at Eagle Crater: a little different in mineralogy, a little
different in color. It may give us the first hint of what the
environment was like before the conditions that produced the Eagle
Crater rocks.”
Inside Endurance Crater are multiple layers of exposed rocks that
might provide information about a much longer period of environmental
history. From the viewpoints around the rim, Opportunity’s miniature
thermal emission spectrometer is returning data for mapping the
mineral composition of the rocks exposed in the crater’s interior.
“We see the coarse hematite grains on the upper slopes and basaltic
sand at the bottom,” said Dr. Phil Christensen of Arizona State
University, Tempe, lead scientist for that spectrometer. “Most
exciting is the basalt signature in the layered cliffs.” Basalt is
volcanic in origin, but the thinness of the layers visible in the
cliffs suggests they were emplaced some way other than as flows of
lava, he said.
“Our working hypothesis is that volcanically erupted rock was broken
down into particles that were then transported and redeposited by wind
or by liquid water,” Christensen said.
At a press conference today in Montreal, Canada, Christensen and
Squyres presented previews of rover-science reports scheduled this
week at a joint meeting of the American Geophysical Union and the
Canadian Geophysical Union.
Although the stack of rock layers at Endurance is more than 10 times
thicker than the bedrock exposure at Eagle Crater, it is still only a
small fraction of the 200-meter-thick (650-foot-thick) stack seen from
orbit at some other locations in Mars’ Meridian Planum region. A
close-up look at the Endurance Crater rocks could help with
interpreting the other exposures seen from orbit. “It’s possible that
the whole stack was deposited in water — some particles washed in by
flowing water and others chemically precipitated out of the water,”
Christensen said. “An alternative is that wind blew sand in.”
Halfway around Mars from Opportunity, Spirit is driving toward
highlands informally named “Columbia Hills,” where scientists hope to
find older rocks than the ones on the plain the rover has been
crossing. The rover could reach the edge of the hills by mid-June.
“Spirit is making breathtaking progress,” Squyres said. “The other day
it covered 124 meters [407 feet] in one day. And that’s not a parking
lot we’re crossing. It’s hilly, rock-strewn terrain. This kind of
pace bodes well for having lots of rover capability left when we get
to the hills.”
