​There's a New Test for Life on Mars, and It's More Accurate Than Ever

The question of whether Mars has ever hosted life has been speculated about for centuries, but the answer been only thrust within reach within the last few decades. Indeed, both the Viking landers and the Curiosity rover have stumbled across the organic compound chloromethane on the planet, which could have been formed by life native to Mars.

Frustratingly, however, chloromethane is far from a smoking gun for Martian biology. It's well-documented that this compound was able to form completely abiotically in the meteorites of the early solar system, so the samples Viking and Curiosity picked up may just be debris from these meteorite impacts.

Another possibility is that trace amounts of chloromethane hitchhiked on spacecraft from Earth. The sterilization process for Martian landers is exhaustive, but until scientists are able to definitively claim that the compound originated on Mars, terrestrial contamination will remain a plausible explanation for its presence there.

Fortunately, there may be a way to isolate which of these three scenarios produced Mars's chloromethane. A team of geoscientists based out of the University of Heidelberg conducted an isotope analysis of the Murchison meteorite, which landed near Murchison, Australia, in 1969. The results were published today in Scientific Reports, and indicate that identifying the isotopic signature of chloromethane could be the key to unlocking its origin.

"We suggest that for future Mars missions, the isotopic fingerprint of the chloromethane could determine whether its origin is from organic material that is indigenous to Mars, deposited by meteorites, or contamination from the landers sent from Earth," lead author Frank Keppler told me.

Keppler and his colleagues used the Murchison meteorite to figure out the properties of extraterrestrial chloromethane, compared to its terrestrial signature. If the instruments they used to read the compound's alien "fingerprint" were sent to Mars, it could differentiate between chloromethane samples that originated on Earth, and those that came from meteorites or, potentially, biological processes.

Keppler thinks the meteorite option is most likely, but would not rule out the possibility that Martian lifeforms may have contributed to the compound's relative abundance. "It can be not excluded that microorganisms which might have been living on the planet some time ago have provided a fraction of the organic matter," he told me.

Unfortunately, the instrument that studies chloromethane on Curiosity's Mars Science Laboratory is not capable of conducting isotopic analysis with this precision, so this technique will have to wait for the next departure to our brother planet. But in the meantime, Keppler's team will be busy studying the compound's relationship with our own world.

"My group focuses on the formation of greenhouse and ozone depleting gases on Earth," Keppler said. "This has helped us very much to explain methane and chloromethane formation on Mars formation."

"We have recently made contact [with] some NASA scientists […] who investigate the occurrence of life in Mars-like environments on Earth such as Antarctic Dry Valleys and the Atacama Desert," he continued. "We might look for chloromethane formation in those environments."

Once again, the Earth proves itself to be the the best astrobiological laboratory at our disposal. Understanding how complex organic compounds like chloromethane form here will inform how they form elsewhere in the solar system, and that may be the key to solving the longstanding mystery of life on Mars.