The NASA Hubble Space Telescope used the Earth as a proxy for identifying oxygen on potentially habitable exoplanets orbiting other stars. During the eclipse, astronomers used Hubble to detect Earth’s ozone in the atmosphere. The method simulates how astronomers and other researchers can search for life beyond Earth by observing potential biosignatures.
The process astronomers used didn’t look directly at the Earth with Hubble. Instead, the astronomers used the moon as a mirror to reflect sunlight that had passed through Earth’s atmosphere and was reflected towards the telescope. The method reproduced the conditions under which future telescopes would measure atmospheres of transiting exoplanets.
This was the first time that a total lunar eclipse was captured at ultraviolet wavelengths from a space telescope. Hubble can detect the strong spectral fingerprint of ozone, which absorbs some of the sunlight that hits the Earth. Ozone is critical to life on Earth as it is the planet’s protective shield.
Researchers say that the atmospheres of some extrasolar planets can be scanned if the world passes across the parent star’s face. During a transit starlight filters through the backlit atmosphere of the planet and chemicals in the atmosphere leave a signature by filtering out certain starlight colors.
So far, astronomers have observed the atmospheres of gas giant planets and the super-Earths that transit their stars using this technique. However, the researchers admit that finding similar signatures from Earth-sized exoplanets will be much more difficult.