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Hubble demonstrates how to see exoplanet atmospheres by using lunar eclipse

The Hubble Space Telescope has demonstrated a new method which could be used to learn more about exoplanets, by observing a total lunar eclipse from space.

Astronomers thought it might be possible to test out a new detection method by experimenting with Hubble. When the Earth passes exactly between the sun and the moon in a lunar eclipse, the moon is blocked out by its shadow. A similar thing happens when an exoplanet passes between the Earth and a distant star.

So the astronomers checked whether they could determine facts about the Earth by observing the moon, using it as a mirror and seeing how it reflects sunlight. The light had passed through Earth’s atmosphere, which filters it, and by observing the reflected light from the moon they could make inferences about Earth.

astronomers using the NASA/ESA Hubble Space Telescope have measured the amount of ozone in Earth’s atmosphere
Taking advantage of a total lunar eclipse in January 2019, astronomers using the NASA/ESA Hubble Space Telescope have measured the amount of 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 ESA/Hubble, M. Kornmesser

Using this method, they were able to detect the presence of ozone in Earth’s atmosphere, just by observing the moon. This is significant because ozone is related to the presence of life, with most of the ozone in our atmosphere created by photosynthesis and the gas playing an important part in protecting the Earth from cosmic radiation.

If this method was used to observe exoplanets, we might be able to spot ozone there as well. “Finding ozone in the spectrum of an exo-Earth would be significant because it is a photochemical byproduct of molecular oxygen, which is a byproduct of life,” Allison Youngblood of the Laboratory for Atmospheric and Space Physics, lead researcher of Hubble’s observations, explained in a statement.

Future space telescopes such as the upcoming James Webb Space Telescope could use this method to investigate the atmosphere of exoplanets including rocky Earth-like planets, something which is very hard to do with current telescopes and methods. It could even give clues to where to investigate first when searching for potentially habitable planets. For now, this study acts as a proof of the concept when looking at our own planet.

“To fully characterize exoplanets, we will ideally use a variety of techniques and wavelengths,” team member Antonio Garcia Munoz of the Technische Universität Berlin in Germany said in the statement. ”This investigation clearly highlights the benefits of the ultraviolet spectroscopy in the characterization of exoplanets. It also demonstrates the importance of testing innovative ideas and methodologies with the only habitable planet that we know of to date!”

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