Taking advantage of a total lunar eclipse, astronomers used NASA’s Hubble Space Telescope and detected Earth’s own brand of sunscreen — ozone — in our atmosphere. This method essentially simulates how astronomers and astrobiology researchers would search for evidence of life beyond Earth by observing potential “biosignatures” on exoplanets that are planets around other stars. However, the Hubble did not look at Earth directly, but, instead, the astronomers used the Moon as a mirror to reflect sunlight, which had passed through Earth’s atmosphere, and then reflected back towards Hubble. 

Using a space telescope for eclipse observations reproduces the conditions under which future telescopes would measure atmospheres of transiting exoplanets. These atmospheres may contain chemicals of interest to astrobiology, the study of and search for life.

“Finding ozone is significant because it is a photochemical byproduct of molecular oxygen, which is itself a byproduct of life,” Allison Youngblood of the Laboratory for Atmospheric and Space Physics in Boulder, Colorado, Lead Researcher of Hubble’s observations, said in a statement.

Even as the ozone in Earth’s atmosphere had been detected in previous ground-based observations during lunar eclipses, Hubble’s study represents the strongest detection of the molecule to date because ozone — as measured from space with no interference from other chemicals in the Earth’s atmosphere — absorbs ultraviolet light so strongly.