Standing Body of Water Left Its Mark in Mars Rocks
March 23, 2004
NASA’s Opportunity rover has demonstrated some rocks on Mars probably
formed as deposits at the bottom of a body of gently flowing saltwater.
Evidence for Underwater Origin Interpretations of cross-lamination
patterns presented as clues to this martian rock’s origin
under flowing water are marked on this image taken by
the panoramic camera and microscopic imager on NASA’s
think Opportunity is parked on what was once the shoreline of
a salty sea on Mars," said Dr. Steve Squyres of Cornell University,
Ithaca, N.Y., principal investigator for the science payload on
Opportunity and its twin Mars Exploration Rover, Spirit.
gathered so far do not tell how long or how long ago liquid water
covered the area. To gather more evidence, the rover’s controllers
plan to send Opportunity out across a plain toward a thicker exposure
of rocks in the wall of a crater.
Associate Administrator for Space Science Dr. Ed Weiler said,
"This dramatic confirmation of standing water in Mars’ history
builds on a progression of discoveries about that most Earthlike
of alien planets. This result gives us impetus to expand our ambitious
program of exploring Mars to learn whether microbes have ever
lived there and, ultimately, whether we can."
patterns in some finely layered rocks indicate the sand-sized
grains of sediment that eventually bonded together were shaped
into ripples by water at least five centimeters (two inches) deep,
possibly much deeper, and flowing at a speed of 10 to 50 centimeters
(four to 20 inches) per second," said Dr. John Grotzinger,
rover science-team member from the Massachusetts Institute of
Technology, Cambridge, Mass.
telltale patterns, called crossbedding and festooning, some layers
within a rock lie at angles to the main layers. Festooned layers
have smile-shaped curves produced by shifting of the loose sediments’
rippled shapes under a current of water.
that formed in wind look different than ripples formed in water,"
Grotzinger said. "Some patterns seen in the outcrop that
Opportunity has been examining might have resulted from wind,
but others are reliable evidence of water flow.”
to Grotzinger, the environment at the time the rocks were forming
could have been a salt flat, or playa, sometimes covered by shallow
water and sometimes dry. Such environments on Earth, either at
the edge of oceans or in desert basins, can have currents of water
that produce the type of ripples seen in the Mars rocks.
second line of evidence, findings of chlorine and bromine in the
rocks, also suggests this type of environment. Rover scientists
presented some of that news three weeks ago as evidence the rocks
had at least soaked in mineral-rich water, possibly underground
water, after they formed. Increased assurance of the bromine findings
strengthens the case that rock-forming particles precipitated
from surface water as salt concentrations climbed past saturation
while water was evaporating.
James Garvin, lead scientist for Mars and lunar exploration at
NASA Headquarters, Washington, said, "Many features on the
surface of Mars that orbiting spacecraft have revealed to us in
the past three decades look like signs of liquid water, but we
have never before had this definitive class of evidence from the
martian rocks themselves. We planned the Mars Exploration Rover
Project to look for evidence like this, and it is succeeding better
than we had any right to hope. Someday we must collect these rocks
and bring them back to terrestrial laboratories to read their
records for clues to the biological potential of Mars."
said, "The particular type of rock Opportunity is finding,
with evaporite sediments from standing water, offers excellent
capability for preserving evidence of any biochemical or biological
material that may have been in the water."
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., expect
Opportunity and Spirit to operate several months longer than their
initial three-month prime missions on Mars. To analyze hints of
crossbedding, mission controllers programmed Opportunity to move
its robotic arm more than 200 times in one day, taking 152 microscope
pictures of layering in a rock called "Last Chance."
a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover Project for NASA’s Office of
Space Science, Washington. Images and additional information about
the project are available on the Internet at http://www.nasa.gov,
Mineral in Mars ‘Berries’ Adds to Water Story
microscopic image, taken at the outcrop region dubbed "Berry
Bowl" near the Mars Exploration Rover Opportunity’s
landing site, shows the sphere-like grains or "blueberries"
that fill Berry Bowl.
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.
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.
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 Mössbauer
spectrometer, which identifies iron-bearing minerals, found a big
difference between the batch of spherules and a "berry-free"
area of the underlying rock.
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.
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,
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.
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
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.
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,
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
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
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.