…The instrument, called a gas chromatograph-mass spectrometer (GC-MS), has been installed on Martian probes since the mid-1970s with early versions on the Viking I and Viking II landers. Solomon and Mark determined that it could be used to detect a chemical bond within cell membrane molecules that are found in many living, and very recently deceased, organisms.
“Space Agencies such as NASA and ESA don’t know their instruments can already do this,” said Professor Sephton. “Here we have developed an elegant method that rapidly and reliably identifies a chemical bond that shows the presence of viable life,” he says. “The Curiosity rover just turned 13 on Mars, but who says you can’t teach an old dog new tricks.”
The new method detects a unique sequence of atoms that bind the constituent molecules of the external membranes of living bacteria and eukarya cells. These constitute the vast majority of biological matter on Earth and include the kinds of lifeforms the scientists would also expect to find beyond our planet.
The signatures of these bonds found in molecules called intact polar lipids (IPLs) show up as a clear spike in a graph produced by the GC-MS instrument (see figure).
Solomon says: “When we put the intact polar lipid compounds into our GC-MS we didn’t know what to expect because these compounds are usually analysed using other techniques. The characteristic signature we identified provides a clear indicator of viable life using space-ready equipment already in use on many extraterrestrial missions. If we find signs of life beyond Earth, the first question will be: is it living right now? It’s thrilling to think that the technique we developed here could be used to help answer that question.”
Once an organism dies, its IPL bonds disintegrate within hours, after which time they can no longer be detected, and a spike no longer appears in the instrument readout.
The method is not only useful for detecting life elsewhere in the solar system but also for protecting life back here on Earth. Groups of scientists from around the world are planning to spend multiple millions of dollars, to detect signs of active life in samples returned from Mars. Their task will be made easier with a quick and simple method to screen for life.
Professor Sephton says, “Our active life detection method could be deployed on Mars and the plumes of icy moons in the outer solar system from where the data can be sent back to Earth for interpretation, or in samples returned to Earth from potential alien biospheres.”
Solomon says: “Our expectation of finding things alive on the Martian surface is low due to the hostile temperature and radiation conditions. Still, we aren’t ruling out the possibility – life finds amazing ways to survive in extreme circumstances. Furthermore, future missions such as the ExoMars mission plan to drill metres deep into the surface of the planet where the likelihood of finding active life is significantly higher.”