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.
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