A New Tool to Detect Alien Biochemistry

Life detection on Mars and the icy moons of the outer Solar System looks more and more feasible.

Sand grains or microbes? In this case, it's a cluster of E. coli bacteria. But it can be hard to tell, so we'll need discerning new instruments. (USDA Photo by Eric Erbe, digital colorization by Christopher Pooley)
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Alberto Fairén and his colleagues from the Centro de Astrobiología in Madrid, Spain, have developed a new tool to detect life on other planets called CMOLD (Complex Molecules Detector), which they outline in a new paper in the journal Astobiology. In so doing, they’ve tackled one of the major scientific challenges in planetary exploration: how to identify life on an alien planet using only a robotic lander mission.

Nearly all previous life detection instruments have looked for volatile organic compounds using a gas chromatograph–mass spectrometer, or GC-MS. The Viking landers of the 1970s, the Curiosity rover now on Mars, and the upcoming European ExoMars mission all carry these devices, which heat up samples to separate their constituent elements and identify them by their spectral signals.

CMOLD does things a little differently. It extracts organic molecules in a liquid suspension and applies three powerful analytical techniques: (1) a microscope to look for microscale visual evidence of life; (2) a Raman spectrometer to detect atomic composition and organic molecules; and (3) a biomarker detector containing antibodies and short DNA and RNA molecules that bind to life-related compounds.

This new technique is very timely. It could make robotic life detection missions to alien worlds more competitive with sample return campaigns such as the one NASA just kicked off with the launch of the Perseverance rover to Mars. Parts of CMOLD have already been extensively tested, and are planned to fly on upcoming missions. For example, the Raman spectrometer is part of the science payload on the European Space Agency’s Rosalind Franklin rover scheduled for launch in 2022. The biomarker detector was included as a payload on a Mars mission proposed to NASA several years ago, called Icebreaker. Considering this heritage, and the amount of testing that’s already been done, Fairén and his colleagues believe the three-part CMOLD could be ready for flight in the very near future.

The authors claim that their new instrument is also suitable for detecting life as we don’t know it. This, of course, depends on just how alien it is. I doubt that the biomarker detector would give positive signals for a very different kind of biochemistry than we have on Earth. But the Raman spectrometer is able to detect complex organic biosignatures even if they don’t correspond to known life molecules. And the high-resolution optical microscope is an invaluable tool for looking closely at any sample.

Thus, CMOLD represents a very promising approach to searching for life on worlds like Mars and the icy satellites Europa and Enceladus, where biology, if it exists, is expected to be at least somewhat similar to what we see on Earth (unlike Titan, which may have an entirely different kind of biochemistry). As we keep formulating missions for planetary exploration, it will be nice to have instruments like CMOLD ready on the shelf.

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