Scientists at the Massachusetts Institute of Technology have developed a new spectroscopic technique that could help uncover signs of life on Mars.
NASA is aiming to launch its newest Mars rover in 2020, with the aim of searching a region of the Red Planet for evidence of ancient microbial life.
The Mars 2020 rover’s job will be to collect samples or rocks and soil for later return to Earth to be studied for signs of life. However, one of the biggest challenges facing the rover is the risk that it could select sediments whose histories have been whitewashed by geological processes. The new method would help the rover quickly identify any unaltered samples and store them for future analysis.
The technique is called Raman spectroscopy and is used on Earth by geologists to identify the chemical composition of rocks. The Mars rover will be equipped with an instrument called SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals), which will enable it to carry out the process.
Raman spectroscopy relies on the principle that atoms and molecules vibrate at different frequencies according to what they are bound to, meaning the measurement of these vibrations can reveal the makeup of a sample of rock, for example. In the case of testing on Mars, the technique would be used to determine whether a sample contains carbonaceous matter, which may indicate signs of life. What’s more, the analysis can be done non-invasively and without damaging the sample.
Roger Summons, professor of earth, atmospheric and planetary sciences at MIT has raised an issue with the technique; namely that Raman spectroscopy does not always produce clear results. A Raman spectrum of a piece of coal on Earth, for example, could look similar to a particle in a meteorite from space.
“We don’t have a way to confidently distinguish between organic matter that was once biological in origin, versus organic matter that came from some other chemical process,” he says.
A research scientist at MIT named Nicola Ferralis has been working on a way around this problem. She found that peaks in Raman spectra could be used to estimate the ration of hydrogen to carbon atoms in samples. This is useful because the more heating a rock experiences, the more hydrogen is lost in the form of methane. Therefore, being able to decipher the hydrogen-carbon ratio in a sample could tell scientists whether that sample has been geologically altered, or whether it is a pristine sample ripe for study.
“This may help in deciding what samples the 2020 rover will archive,” Summons says. “It will be looking for organic matter preserved in sediments, and this will allow a more informed selection of samples for potential return to Earth.”