Missing Piece Inspires New Look at Mars Puzzle (Phoenix, Viking)


Missing Piece Inspires New Look at Mars Puzzle
Jet Propulsion Laboratory
September 03, 2010

PASADENA, Calif. -- Experiments prompted by a 2008 surprise from NASA's
Phoenix Mars Lander suggest that soil examined by NASA's Viking Mars
landers in 1976 may have contained carbon-based chemical building blocks
of life.

"This doesn't say anything about the question of whether or not life has
existed on Mars, but it could make a big difference in how we look for
evidence to answer that question," said Chris McKay of NASA's Ames
Research Center, Moffett Field, Calif. McKay coauthored a study
published online by the Journal of Geophysical Research - Planets,
reanalyzing results of Viking's tests for organic chemicals in Martian

The only organic chemicals identified when the Viking landers heated
samples of Martian soil were chloromethane and dichloromethane --
chlorine compounds interpreted at the time as likely contaminants from
cleaning fluids. But those chemicals are exactly what the new study
found when a little perchlorate -- the surprise finding from Phoenix --
was added to desert soil from Chile containing organics and analyzed in
the manner of the Viking tests.

"Our results suggest that not only organics, but also perchlorate, may
have been present in the soil at both Viking landing sites," said the
study's lead author, Rafael Navarro-Gonzalez of the National Autonomous
University of Mexico, Mexico City.

Organics can come from non-biological or biological sources. Many
meteorites raining onto Mars and Earth for the past 5 billion years
contain organics. Even if Mars has never had life, scientists before
Viking anticipated that Martian soil would contain organics from meteorites.

"The lack of organics was a big surprise from the Vikings," McKay said.
"But for 30 years we were looking at a jigsaw puzzle with a piece
missing. Phoenix has provided the missing piece: perchlorate. The
perchlorate discovery by Phoenix was one of the most important results
from Mars since Viking." Perchlorate, an ion of chlorine and oxygen,
becomes a strong oxidant when heated. "It could sit there in the Martian
soil with organics around it for billions of years and not break them
down, but when you heat the soil to check for organics, the perchlorate
destroys them rapidly," McKay said.

This interpretation proposed by Navarro-Gonzalez and his four co-authors
challenges the interpretation by Viking scientists that Martian organic
compounds were not present in their samples at the detection limit of
the Viking experiment. Instead, the Viking scientists interpreted the
chlorine compounds as contaminants. Upcoming missions to Mars and
further work on meteorites from Mars are expected to help resolve this

The Curiosity rover that NASA's Mars Science Laboratory mission will
deliver to Mars in 2012 will carry the Sample Analysis at Mars (SAM)
instrument provided by NASA Goddard Space Flight Center, Greenbelt, Md.
In contrast to Viking and Phoenix, Curiosity can rove and thus analyze a
wider variety of rocks and samples. SAM can check for organics in
Martian soil and powdered rocks by baking samples to even higher
temperatures than Viking did, and also by using an alternative
liquid-extraction method at much lower heat. Combining these methods on
a range of samples may enable further testing of the new report's
hypothesis that oxidation by heated perchlorates that might have been
present in the Viking samples was destroying organics.

One reason the chlorinated organics found by Viking were interpreted as
contaminants from Earth was that the ratio of two isotopes of chlorine
in them matched the three-to-one ratio for those isotopes on Earth. The
ratio for them on Mars has not been clearly determined yet. If it is
found to be much different than Earth's, that would support the 1970s

If organic compounds can indeed persist in the surface soil of Mars,
contrary to the predominant thinking for three decades, one way to
search for evidence of life on Mars could be to check for types of
large, complex organic molecules, such as DNA, that are indicators of
biological activity. "If organics cannot persist at the surface, that
approach would not be wise, but if they can, it's a different story,"
McKay said.

The Phoenix mission was led by Principal Investigator Peter H. Smith of
the University of Arizona, Tucson, with project management at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. The Phoenix finding of
perchlorate was reported by JPL's Michael Hecht and co-authors. JPL, a
division of the California Institute of Technology, Pasadena, also
manages Mars Science Laboratory for the NASA Exploration Missions
Directorate, Washington.

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

Rachel Hoover/Ruth Marlaire 650-604-0643/650-604-4709
Ames Research Center, Moffett Field, Calif.

Gabriela Frias 011-52-55-5622-4684
Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de
Mexico, Mexico City