The search
for past life on Mars just got a new tool in its tool belt with an instrument
that zaps bits of minerals off rocks and analyzes those pieces for the remains
of living cells.
NASA
orbiters and rovers have found abundant evidence that liquid water
once flowed on the surface of Mars, and that evidence of water raises the
possibility that the red planet once harbored life, even if only
tiny microbes.
Other
missions have looked at the question of life on Mars more directly. The U.S. Viking
missions of the 1970s and '80s tested Martian dirt for life directly, but
didn't find it. NASA's Phoenix
Mars Lander is approaching the end of its mission to analyze the ice-rich
dirt of Mars' arctic region for signs of organics.
But what
scientists would really love is to get their hands on a sample of Mars and
bring it back to Earth. That's where this instrument, which is being developed
by researchers at the Idaho National Laboratory (INL), would come in.
How it
works
The
instrument uses a "point-and-shoot" laser technique called laser
desorption mass spectroscopy to analyze mineral samples. The researchers focus
a laser beam on a spot less than one-hundredth the width of a pencil point and
the laser knocks off microscopic fragments of the mineral.
If there
are any organics in the sample, the mineral fragments react with them to form
ions (atoms or molecules that have lost or gained an electron). The
instrument's mass spectrometer can detect the ions and the team can study the
pattern they create to see if it shows any signatures that could belong to
specific biomolecules.
With
funding from NASA's Astrobiology program, INL's Jill Scott and her team have
been running tests with the instrument and what she calls "Earth analogs
of Martian rocks" to see which minerals are the best bets for finding a
strong signal in a Martian sample. It will also give future
missions to Mars a guideline for what minerals to pick up and bring home;
Scott's team will be able to tell NASA, "Here's your most promising
choices. Go after these."
"Some
minerals just don't work well," Scott said. Iron oxides
particularly don't work, which Scott said is "too bad" because Mars
is what she calls "the rust planet."
So far,
halite (or rock salt) and jarosite give distinct patterns when zapped if they
have organic molecules in them. The team has also tested thenardite samples
take from the evaporated Searles Lake bed in California. Thenardite is thought
to be a component of the Martian surface and because it is left behind when
lakes dry up, its presence could in a sample could mean that water — and hence
life — was once present in the area.
Scott and
her team also created artificial thenardite samples containing traces of
stearic acid, which is left behind by dead cells, and glycine, the simplest
amino acid used by life on Earth. (Amino acids are the building blocks of
proteins.)
All of the
experiments showed a distinct ion pattern that didn't appear when thenardite
was tested alone, suggesting that the pattern was showing a signature of the
added biomolecules.
The
biomolecules could be detected at concentrations as low as 3 parts per trillion,
the researchers recently reported in the Geomicrobiology Journal. Such
high sensitivity is crucial to the search for signs of life on Mars because
those signs could be very small.
"They're
probably going to be few and far-between," Scott said.
NASA is
planning on flying a different laser to zap rocks on the upcoming Mars
Science Laboratory mission. The laser will also give of dust that can be
analyzed by mass spectrometers to learn their composition.
Why it's
better
There are
other techniques that can detect organics in rocks, but they require extracting
the organic material from samples, which can be "very sample-consuming and
time consuming," Scott said.
You can
only bring so many samples back from Mars, and you don't want to waste what you
have, Scott said.
These other
methods would also be impractical to do on Mars itself because of all the
sample preparation involved.
"If
you're going to be doing this on Mars, you're not going to want to do sample
preparation, Scott said.
Scott and
her team would like to work on making the instrument smaller so that it could
be sent to Mars, opening up the sampling possibilities, but for now they lack
the funding.
They are
also working to improve the laser on the instrument, which is now only ionizing
about 10 percent of all the biomolecules in a sample. This step would improve
the instrument's detection capabilities.
"There's
still a lot to be done," Scott said.
advertisement
