One way to search for extraterrestrial life is to look for tell-tale signs of biology in the atmospheres of planets orbiting other star systems. Such a “biosignature” that shows the simultaneous presence of oxygen, water vapor, and methane, for example, would be consistent with the presence of surface life on a planet. Observing biosignatures on other planets is a difficult feat, but current and future ground- and space-based telescopes are gradually enabling these observations.

Another place to build a telescope for observing biosignatures is the moon. Stoney Simons and I explore this idea in a recent paper titled “A trip to the moon might constrain the Fermi Paradox,” which is part of the Futures special issue on the Detectability of Future Earth. The moon’s negligible atmosphere makes observations much easier than ground-based astronomy, particularly at the mid-infrared wavelengths needed to detect possible biosignatures.

Searching for biosignatures in the infrared provides a quantitative method of constraining the abundance of life in the galaxy. Likewise, the possibility of observing “technosignatures” in the atmospheres of distant planets could betray the presence of extraterrestrial intelligence. Actually finding any definitive biosignatures or technosignatures will require at least a couple more decades of observing, but we suggest that a lunar observatory should remain an option for contributing to this search.