NASA Mars Rovers Head for New Sites After Studying Layers

PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown/Erica Hupp (202) 358-1726/1237
NASA Headquarters, Washington

News Release: 2006-054 April 12, 2006

NASA Mars Rovers Head for New Sites After Studying Layers

NASA’s Mars rover Spirit has reached a safe site for the
Martian winter, while its twin, Opportunity, is making
fast progress toward a destination of its own.

The two rovers recently set out on important – but very
different – drives after earlier weeks inspecting sites
with layers of Mars history. Opportunity finished
examining sedimentary evidence of ancient water at a
crater called “Erebus,” and is now rapidly crossing flat
ground toward the scientific lure of a much larger crater,

Spirit studied signs of a long-ago explosion at a bright,
low plateau called “Home Plate” during February and March.
Then one of its six wheels quit working, and Spirit
struggled to complete a short advance to a north-facing
slope for the winter. “For Spirit, the priority has been
to reach a safe winter haven,” said Dr. Steve Squyres of
Cornell University, Ithaca, N.Y., principal investigator
for the Mars Exploration Rover project.

The rovers have operated more than eight times as long
as their originally planned three-month explorations on
Mars. Each has driven more than 6.8 kilometers (4.2
miles) about 11 times as far as planned. Combined, they
have returned more than 150,000 images. Two years ago,
the project had already confirmed that at least one place
on Mars had a wet and possibly habitable environment long
ago. The scientific findings continue.

Opportunity spent most of the past four months at Erebus,
a highly eroded impact crater about 300 meters (1,000 feet)
in diameter, where the rover found extensive exposures of
thin, rippled layering interpreted as a fingerprint of
flowing water. “What we see at Erebus is a thicker
interval of wetted sediment than we’ve seen anywhere
else,” said Dr. John Grotzinger of the California
Institute of Technology, “The same outcrops also have
cracks that may have formed from wetting and drying.”

In mid-March, Opportunity began a 2-kilometer (1.6-mile)
trek from Erebus to Victoria, a crater about 800 meters
(half a mile) across, where a thick sequence of
sedimentary rocks is exposed. In the past three weeks,
Opportunity has already driven more than a fourth of
that distance.

At Home Plate, Spirit found coarse layering overlain by
finer layering in a pattern that fits accumulation of
material falling to the ground after a volcanic or
impact explosion. In one place, the layers are deformed
where a golfball-size rock appears to have fallen on
them while they were soft.

“Geologists call that a ‘bomb sag,’ and it is strong
evidence for some kind of explosive origin,” Squyres
said. “We would like to have had time to study Home
Plate longer, but we needed to head for a north-facing
slope before winter got too bad.”

Spirit is in Mars’ southern hemisphere, where the sun
is crossing lower in the northern sky each day. The
rovers rely on solar power. The amount available will
keep dropping until the shortest days of the Mars winter,
four months from now. To keep producing enough
electricity to run overnight heaters that protect vital
electronics, Spirit’s solar panels must be tilted toward
the winter sun by driving the rover onto north-facing
slopes. However, on March 13 the right-front wheel’s
drive motor gave out. Spirit has subsequently driven
about 80 meters (262 feet) using five wheels and
dragging the sixth, but an initial route toward a large
hill proved impassable due to soft ground. Last week,
the team chose a smaller nearby ridge, dubbed “Low Ridge
Haven,” as the winter destination. Spirit reached the
ridge Sunday and has a favorable 11-degree tilt toward
the north.

“We have to use care choosing the type of terrain we
drive over,” Dr. Ashitey Trebi-Ollennu, a rover planner
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.,
said about the challenge of five-wheel driving. In tests
at JPL, the team has been practicing a maneuver to gain
additional tilt by perching the left-front wheel on a
basketball-size rock.

Spending eight months or so at Low Ridge Haven will
offer time for many long-duration studies that members
of the science team have been considering since early
in the mission, said Dr. Ray Arvidson of Washington
University in St. Louis, deputy principal investigator.
These include detailed mapping of rocks and soils;
in-depth determination of rock and soil composition;
monitoring of clouds and other atmospheric changes;
watching for subtle surface changes due to winds; and
learning properties of the shallow subsurface by
tracking surface-temperature changes over a span of

JPL, a division of the California Institute of
Technology, Pasadena, manages the Mars Exploration
Rover Project for the NASA Science Mission Directorate.

For images and information about the rovers, see or .

For information about NASA and agency programs on the
Web, visit .