Mars Rover Inspects Stone Ejected From Crater
May 17, 2004
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."
JPL, a division of the California Institute of Technology in
Pasadena, manages the Mars Exploration Rover project for
NASA's Office of Space Science, Washington, D.C. Images and
additional information about the project are available from
JPL at http://marsrovers.jpl.nasa.gov and from Cornell
University at http://athena.cornell.edu.
