Searching for alien life in the vast expanse of the universe is somewhat comparable to tracking animals here on Earth. Astronomical observatories scan the depths of space for compounds associated with life (called "biomarkers"), much like wildlife experts read tracks and markings. But while a footprint is a relatively clear calling card of a living creature, biomarker compounds like oxygen, methane, or hydrocarbons could be produced either by life, or by abiotic processes.
Astronomers have suggested that chloromethane (CH3Cl), an organohalogen compound known as Freon-40, could be a potentially valuable biomarker in the search for extraterrestrial life. On Earth, chloromethane is emitted by tropical plants, plankton, and peat bog ecosystems, and detection of this compound on Mars by the Viking and Curiosity missions ignited years of unresolved debate about whether the samples were biological or geological in origin.
Research published Monday in Nature Astronomy adds a new twist to this astrobiological saga with the detection of chloromethane in two very different extraterrestrial environments: the atmosphere of a comet in our solar system, and an infant star system 400 light years away. This doesn't mean that life exists at these locations, and in fact, the finding dashes the hopes of some scientists who regarded Freon-40 as a relatively solid indicator of biological activity.
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