More than
30 years ago, NASA's Viking life-detection experiments on Mars returned
inconclusive results, and controversy surrounds the Viking data to this day.
The Phoenix mission now on Mars may collect data that will help answer questions raised by
Viking, but to do so researchers will need to be able to spot the difference
between chemical and biological signatures on Mars.
In the mid
1970s, NASA's Viking
Landers analyzed material from the Martian surface in the hopes of finding
signatures of life. The Viking life-detection experiments indicated the presence
of oxidized organic material near the surface. At first, researchers on the
instrument team believed this was evidence of biological activity on Mars.
However,
other scientists immediately criticized the results. Eventually, the scientific
community decided that it was more likely the organic material had been
oxidized by the chemical hydrogen
peroxide, which was detected at the surface by the Viking Gas Exchange
experiment.
Not
everyone is satisfied with this explanation. There are still questions about
where hydrogen peroxide on Mars comes from, how long it can naturally remain
stable at the surface and how much is actually present.
New
answers
An answer
may be on the horizon.
NASA's Phoenix
Lander touched down on Mars on May 25. Onboard is an instrument called the
Thermal and Evolved Gas Analyzer (TEGA), which will be used to analyze soil and
ice samples on Mars. The instrument could help explain the puzzling Viking
results.
In order to
prepare for the Phoenix experiments, a team of researchers performed a series
of tests. They simulated the experiments to be conducted by Phoenix to
determine what the results would look like if microbes were present in martian
soil. Researchers inoculated simulated martian soil with known Earth-organisms
that can survive in the presence of hydrogen peroxide. (On Earth, some microbes
produce hydrogen peroxide and others are able to utilize it.)
Unique
Mars microbes
Mixtures of
water and hydrogen peroxide freeze at much lower temperatures than water alone.
The researchers theorize that microbes might be able to use hydrogen peroxide
to survive at lower temperatures. The idea is based on Earth microbes
that use salts in a similar way, providing them with an "antifreeze"
that keeps them alive in cold environments. If microbes on Mars adapted to use
hydrogen peroxide in a similar way, it may mean that the Viking results need to
be reinterpreted.
By testing
the simulant Martian soil with the TEGA instrument, the research team was able
to identify signatures that indicated microbes. Specific chemicals that can be
detected by TEGA can now serve as biomarkers for possible life on Mars.
The
simulated experiments provide an important test for chemical versus biological
responses in the Phoenix mission. In other words, the Phoenix mission could
provide definitive answers to the questions posed by Viking, and may even tell
us if life exists on Mars.
The research was published in the April 2008 edition of the journal Astrobiology under lead author Dirk Shulze-Makuch.
advertisement
