During the January 2019 total lunar eclipse, astronomers trained the Hubble Telescope on our moon in order to calibrate how future telescopes will look for possible life on exoplanets by measuring ozone levels.
Though numerous ground-based observations of this kind have been done previously, this is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. Hubble detected the strong spectral fingerprint of ozone, which absorbs some of the sunlight. Ozone is important to life because it is the source of the protective shield in Earth's atmosphere.
On Earth, photosynthesis over billions of years is responsible for our planet's high oxygen levels and thick ozone layer. That's one reason why scientists think ozone or oxygen could be a sign of life on another planet, and refer to them as biosignatures.
NASA's James Webb Space Telescope could use infrared in this way to detect atmospheric methane and oxygen following its scheduled 2021 launch.