Mineral in Mars 'Berries' Adds to Water Story
March 18, 2004
A major ingredient in small mineral spheres analyzed by
NASA's Mars Exploration Rover Opportunity furthers
understanding of past water at Opportunity's landing site and
points to a way of determining whether the vast plains
surrounding the site also have a wet history.
The spherules, fancifully called blueberries although they
are only the size of BBs and more gray than blue, lie
embedded in outcrop rocks and scattered over some areas of
soil inside the small crater where Opportunity has been
working since it landed nearly two months ago.
Individual spherules are too small to analyze with the
composition-reading tools on the rover. In the past week,
those tools were used to examine a group of berries that had
accumulated close together in a slight depression atop a rock
called "Berry Bowl." The rover's Moessbauer spectrometer,
which identifies iron-bearing minerals, found a big
difference between the batch of spherules and a "berry-free"
area of the underlying rock.
"This is the fingerprint of hematite, so we conclude that the
major iron-bearing mineral in the berries is hematite," said
Daniel Rodionov, a rover science team collaborator from the
University of Mainz, Germany. On Earth, hematite with the
crystalline grain size indicated in the spherules usually
forms in a wet environment.
Scientists had previously deduced that the martian spherules
are concretions that grew inside water-soaked deposits.
Evidence such as interlocking spherules and random
distribution within rocks weighs against alternate
possibilities for their origin. Discovering hematite in the
rocks strengthens this conclusion. It also adds information
that the water in the rocks when the spherules were forming
carried iron, said Dr. Andrew Knoll, a science team member
from Harvard University, Cambridge, Mass.
"The question is whether this will be part of a still larger
story," Knoll said at a press briefing today at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. Spherules below the
outcrop in the crater apparently weathered out of the
outcrop, but Opportunity has also observed plentiful
spherules and concentrations of hematite above the outcrop,
perhaps weathered out of a higher layer of once-wet deposits.
The surrounding plains bear exposed hematite identified from
orbit in an area the size of Oklahoma -- the main reason this
Meridiani Planum region of Mars was selected as Opportunity's
landing site.
"Perhaps the whole floor of Meridiani Planum has a residual
layer of blueberries," Knoll suggested. "If that's true, one
might guess that a much larger volume of outcrop once existed
and was stripped away by erosion through time."
Opportunity will spend a few more days in its small crater
completing a survey of soil sites there, said Bethany
Ehlmann, a science team collaborator from Washington
University, St. Louis. One goal of the survey is to assess
distribution of the spherules farther from the outcrop. After
that, Opportunity will drive out of its crater and head for a
much larger crater with a thicker outcrop about 750 meters
(half a mile) away.
Halfway around Mars, NASA's other Mars Exploration Rover,
Spirit, has been exploring the rim of the crater nicknamed
"Bonneville," which it reached last week. A new color
panorama shows "a spectacular view of drift materials on the
floor" and other features, said Dr. John Grant, science team
member from the National Air and Space Museum in Washington.
Controllers used Spirit's wheels to scuff away the crusted
surface of a wind drift on the rim for comparison with drift
material inside the crater.
A faint feature at the horizon of the new panorama is the
wall of Gusev Crater, about 80 kilometers (50 miles) away,
said JPL's Dr. Albert Haldemann, deputy project scientist.
The wall rises about 2.5 kilometers (1.6 miles) above
Spirit's current location roughly in the middle of Gusev
Crater. It had not been seen in earlier Spirit images because
of dust, but the air has been clearing and visibility
improving, Haldemann said.
Controllers have decided not to send Spirit into Bonneville
crater. "We didn't see anything compelling enough to take the
risk to go down in there," said JPL's Dr. Mark Adler, mission
manager. Instead, after a few more days exploring the rim,
Spirit will head toward hills to the east informally named
"Columbia Hills," which might have exposures of layers from
below or above the region's current surface.
The main task for both rovers is to explore the areas around
their landing sites for evidence in rocks and soils about
whether those areas ever had environments that were watery
and possibly suitable for sustaining life.
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, Ithaca, N.Y., at http://athena.cornell.edu.
