* Soil analysis shows signs of carbon
* Element is a building block for life
* Could be contamination from Earth
(Recasts, adds details)
By Irene Klotz
SAN FRANCISCO, Dec 3 NASA's Mars rover
Curiosity, dispatched to look for the chemical ingredients and
environments for microbial life, has found hints of carbon,
though whether this building block for life on Earth has played
a similar role on Mars is unknown, scientists said on Monday.
"Just finding carbon somewhere doesn't mean that it has
anything to do with life, or the finding of a habitable
environment," lead scientist John Grotzinger, with the
California Institute of Technology, told reporters at the
American Geophysical Union conference in San Francisco.
"If you have organic carbon and you don't have any water,
you don't have a habitable environment," he said.
Even with carbon and water, life needs other chemicals, such
as sulfur, oxygen, phosphorous and nitrogen, to form and evolve.
"It's not unexpected that this sand pile would not be rich
in organics. It's been exposed to the harsh Martian
environment," added planetary scientist Paul Mahaffy, with
NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"It's really going to be an exciting hunt over the course of
this mission to find early environments that might be protected
from this surface Mars environment and see what we can add to
the carbon story," Mahaffy said.
The rover, which in August touched down on the floor of a
93-mile wide (150-km) impact crater near the Martian equator,
has already turned up evidence that its landing site was once
covered in water.
Scientists do not know if the carbon compounds in the soil
are contamination from Earth, arrived on the surface of Mars via
comets or asteroids, or, if they are indigenous, whether they
came from geological or biological activities on Mars.
"It tells us that we have a lead into a measurement of one
of the important ingredients that adds to a habitable
environment," Grotzinger said. "We still have a lot of work to
do to qualify and characterize what it is."
The rover is expected to reach a richer slice of Martian
history next year when it begins examining layers of sediment in
a mountain rising from the floor of the crater.
"We're starting to find the spices that make a stew tasty.
There are the basic ingredients that you expect to be there, but
it's how you combine them and the minor ingredients that really
turn out to be interesting," he said.
"What this mission is about is integrated science,"
Grotzinger added. "There is not going to be one single moment
where we all stand up and on the basis of a single measurement
have a hallelujah moment."
The rover also carries a radiation detector, intended to
help NASA figure out how much and what type of shielding would
be needed for future planned human missions to Mars, a long-term
goal of the U.S. space program.
Data collected during the rover's four months on the surface
show astronauts would face about the same amount of radiation as
they do aboard the International Space Station, though that
level likely will increase as the sun moves into the more active
phase of its 11-year cycle.
However, astronauts would surpass career radiation limits
imposed by NASA if the higher radiation dosages experienced
during the nine-month cruise to Mars were taken into account,
said Donald Hassler, with the Southwest Research Institute in
"We can survive the Mars surface. The hard part is the
cruise," Hassler said.
The agency is working on spacecraft shielding and protocols
to try to counter the effects of solar and cosmic radiation.
The $2 billion Curiosity mission, which is due to last two
years, is NASA's first astrobiology mission since the 1970s
(Editing by Tom Brown and Jim Loney)