Long-Lived Mars Rover Opportunity Keeps Finding Surprises

NASA’s Mars Exploration Rover Opportunity keeps providing
about the Red Planet, most recently with
observations of possible “rock

The ground texture seen in recent images from the rover
resembles a smudged
version of very distinctive stone stripes
on some mountain slopes on Earth that
result from repeated
cycles of freezing and thawing of wet soil. But it might
be due to wind, downhill transport, other processes or a

Opportunity landed on Mars in January 2004. As it reaches
5,000th Martian
day, or sol, of what was planned as a
90-sol mission, it is investigating a channel called
“Perseverance Valley,” which descends the inboard slope of the
western rim of Endeavour Crater.

“Perseverance Valley is a special place, like having a new
again after all these years,” said Opportunity Deputy
Investigator Ray Arvidson of Washington University
in St. Louis. “We
already knew it was unlike any place any
Mars rover has seen before, even if we
don’t yet know how it
formed, and now we’re seeing surfaces that look like
stripes. It’s mysterious. It’s exciting. I think the set of
we’ll get will enable us to understand it.”

On some slopes within the valley, the soil and gravel particles
to have become organized into narrow rows or
corrugations, parallel to the slope,
alternating between rows
with more gravel and rows with less.

The origin of the whole valley is uncertain. Rover-team
scientists are
analyzing various clues that suggest actions of
water, wind or ice. They are
also considering a range of
possible explanations for the stripes, and remain
about whether this texture results from processes of
modern Mars or a much older Mars.

Other lines of evidence have convinced Mars experts that, on a
scale of
hundreds of thousands of years, Mars goes through
cycles when the tilt or
obliquity of its axis increases so
much that some of the water now frozen at
the poles vaporizes
into the atmosphere and then becomes snow or frost
accumulating nearer the equator.

“One possible explanation of these stripes is that they are
from a time of greater obliquity when snow packs on the
rim seasonally melted
enough to moisten the soil, and then
freeze-thaw cycles organized the small
rocks into stripes,”
Arvidson said. “Gravitational downhill movement
may be
diffusing them so they don’t look as crisp as when they were

Bernard Hallet of the University of Washington, Seattle, agrees
alignments seen in images of Perseverance Valley are not
as distinctive as the
stone stripes he has studied on Earth.
Field measurements on Earth, near the
summit of Hawaii’s Mauna
Kea where the soil freezes every night but is often
dry, have
documented how those form when temperature and ground
conditions are
right: Soils with a mix of silt, sand and
gravel expand more where the
finer-grain material is most
prevalent and retains more water. Freezing expands
the soil,
pushing larger particles up. If they move to the side, as well
down the general slope, due to gravity or wind, they tend
to move away from the
finer-grain concentrations and stretch
out downslope. Where larger particles
become more
concentrated, the ground expands less. The process repeats
or thousands of times, and the pattern self-organizes
into alternating stripes.

Perseverance Valley holds rocks carved by sand blowing uphill
from the
crater floor, and wind might also be the key in
sorting larger particles into
rows parallel to the slope.

“Debris from relatively fresh impact craters is scattered over
surface of the area, complicating assessment of effects of
wind,” said Opportunity
science-team member Robert Sullivan of
Cornell University, Ithaca, New York.
“I don’t know what these
stripes are, and I don’t think anyone else knows
for sure what
they are, so we’re entertaining multiple hypotheses and
more data to figure it out.”

Every sol Opportunity keeps working may add information to help
solve some
puzzles and find new ones. For more information
about Opportunity, visit:



News Media Contact

Guy Webster / Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278 / 818-393-2433
guy.webster@jpl.nasa.gov / andrew.c.good@jpl.nasa.gov

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov