• Scientists observed the Moon using Hubble during a total lunar eclipse
  • They studied Earth's biosignature by using the Moon as a mirror
  • The same method can be used to find exoplanets that can support alien life

Using the Hubble Space Telescope, scientists were able to use the Moon as a mirror during a total lunar eclipse to observe Earth’s atmosphere. According to the scientists, this method can be used to identify exoplanets that have the potential to support organic alien life.

During the total lunar eclipse in January last year, the Hubble, which is operated by NASA and the European Space Agency (ESA), faced the Moon and used it as a mirror to reflect the sunlight that passed through Earth’s atmosphere, which then reflected back to the space telescope.

Through this method, scientists were able to study Earth’s biosignature, which is composed of traces of various compounds in the atmosphere. In the search for exoplanets, studying the biosignatures provides the necessary information in order to determine an alien world’s capability of supporting life.

On Earth, for instance, photosynthesis, the process used by plants to nourish themselves using sunlight, is responsible for the high levels of oxygen on the planet. It also leads to the formation of Earth’s thick ozone layer.

According to scientists, Earth’s oxygen level in the atmosphere and the presence of an ozone layer are among the planet’s main biosignatures.

“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 Colorado and lead author of a study based in Hubble’s findings explained in a statement.

Youngblood noted that the method used by Hubble demonstrated how Earth’s biosignature could be used as a template in finding other exoplanets that could be potentially habitable. Using Earth as the basis for an ideal habitable world, scientists could use the same technique to find exoplanets that have signs of a life.

“One of NASA's major goals is to identify planets that could support life,” Youngblood stated. “But how would we know a habitable or an uninhabited planet if we saw one? What would they look like with the techniques that astronomers have at their disposal for characterizing the atmospheres of exoplanets? That's why it's important to develop models of Earth's spectrum as a template for categorizing atmospheres on extrasolar planets.”

The study conducted by Youngblood was published in The Astronomical Journal.

This illustration shows the Hubble Space Telescope superimposed on an image of the Moon, seen during a lunar eclipse. Taking advantage of a total lunar eclipse in January 2019, astronomers using NASA's Hubble Space Telescope have detected ozone in Earth's atmosphere. This method serves as a proxy for how they will observe Earth-like planets transiting in front of other stars in search of life. Our planet's perfect alignment with the Sun and Moon during a total lunar eclipse mimics the geometry of a transiting terrestrial planet with its star. In a new study, Hubble did not look at Earth directly. Instead, astronomers used the Moon as a mirror that reflects the sunlight transmitted through Earth's atmosphere, which was then captured by Hubble. This is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. M. Kornmesser (ESA/Hubble), NASA, and ESA