* Mars Science Laboratory due to land on Mars on Aug. 6
* It will explore places that could have hosted life
* Focus on geology of mound of sediment inside crater
(Adds new details on landing, paragraph 20)
By Irene Klotz
CAPE CANAVERAL, Fla., June 11 (Reuters) - This summer, if
all goes well, a robotic geologist will arrive on Mars to try
out a new strategy for searching for life beyond Earth.
Rather than hunt for microbes like the Viking missions of
the 1970s, NASA's Mars Science Laboratory, a wheeled rover
nicknamed Curiosity, will look for places that could have hosted
and preserved life.
"The term 'life-detection' is so ill-defined and so hard to
ascertain it doesn't make a good starting point," said geologist
John Grotzinger of the California Institute of Technology, who
is the lead scientist for the Curiosity mission.
Instead, NASA's new Mars mission, scheduled for landing on
Aug. 6, is primarily a geological expedition to an intriguing
piece of real estate called Gale Crater, located just south of
the Martian equator.
Scientists believe the crater formed some 3.5 billion to 3.8
billion years ago when Mars, Earth and the rest of the planets
in the inner solar system were regularly bombarded by
meteorites.
Gale's most striking feature is not the 96-mile (154-km)
wide pit in the ground, but a 3-mile-high a(5-km-high) mound of
debris rising from the crater's floor. Scientists believe the
mountain, located in the center of the basin, is the layered
remains of sediment that once filled the crater.
Over time and by a process not well understood, the sediment
was carried away, leaving what is now known as Mount Sharp,
which scientists hope will reveal the geological history of Mars
like no similar formation can do on Earth.
"There is no place on Earth you can go to get the whole
history at once," Grotzinger told journalists during a field
trip last month to California's Death Valley, one of the few
places where chunks of Earth's geologic record covering large
spans of time are exposed.
"At Gale you don't need to reconstruct the layers. You can
see how they go from older to younger. You've got time's arrow
always pointed in the right direction. It's all laid out very
simply," Grotzinger said.
PRESERVATION OF LIFE
Previous missions to Mars revealed compelling evidence that
the planet was once warmer and wetter than the cold, dry desert
it is today. For example, NASA's Mars Exploration Rovers, one of
which is still operating after more than seven years on the
planet's surface, found minerals that on Earth form only in the
presence of water.
Liquid water is one of three key ingredients needed for life
- at least life as we know it. Life's recipe also requires an
energy source, such as solar or chemical, and a source of
carbon.
"One of the ingredients of life is water. We're now looking
to see if we can find other conditions that are necessary for
life," said Mary Voytek, director of NASA's astrobiology
program.
A key goal for the Mars Science Laboratory is to find
organically produced carbon, a tricky proposition because almost
every process that makes rock destroys organics.
"Even on Earth finding signs of past life isn't easy.
Whatever was happening biologically, if anything, for the first
4 billion years there is no record. For the first 3 billion
years, there's no rock record either," Grotzinger said.
One technique that has proven useful on Earth is to search
for chemistry that can preserve life, a system scientists are
adopting to hunt for signs of life on Mars as well. On early
Earth for example, minerals, such as silica, are important
because they preserved the record of carbon.
"You pickle the organics early on," Grotzinger said.
"Let's assume life did evolve on Mars. Where are the places
that have habitable environments and the highest preservation
potential?" he said. "If you do this as a random walk, you're
doomed to failure because you only have so much time and the
clock is ticking."
If the Mars Science Laboratory touches down safely, which is
by no means a given, scientists expect to have two years to
collect information about Mount Sharp and the surrounding area.
NASA hopes to land the rover on a flat surface as close as
possible to the base of Mount Sharp using a first-of-a-kind,
rocket-powered sky crane. The exact landing spot will depend on
the craft's final steering maneuvers as it races toward Mars.
Mission managers said on Monday they would aim for a 12- by
4-mile (20- by 7-km) patch of land, far smaller than original
estimates, which would shave off months of drive time to reach
the mound.
The rover blasted off aboard an unmanned Atlas 5 rocket on
Nov. 26 for a nine-month, 60-million mile voyage that is due to
end at 1:30 a.m. EDT on Aug. 6.
(Editing by Jane Sutton and Will Dunham)
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