During a transit, starlight filters through the backlit exoplanet’s atmosphere. The atmospheres of some exoplanets can be probed when the alien world passes across the face of its parent star, during a so-called transit. It also demonstrates the importance of testing innovative ideas and methodologies with the only habitable planet that we know of to date!” ” This investigation clearly highlights the benefits of the ultraviolet spectroscopy in the characterization of exoplanets. “ To fully characterize exoplanets, we will ideally use a variety of techniques and wavelengths,” explained team member Antonio Garcia Munoz of the Technische Universität Berlin in Germany. Several other telescopes also made spectroscopic observations at other wavelengths during the eclipse, searching for more of Earth’s life-nurturing ingredients, such as oxygen, methane, water, and carbon monoxide. Hubble recorded ozone’s ultraviolet spectral signature imprinted on sunlight that filtered through Earth’s atmosphere during a lunar eclipse that occurred on 20-21 January, 2019. “ 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,” explained Allison Youngblood of the Laboratory for Atmospheric and Space Physics in Colorado, USA, lead researcher of Hubble’s observations. That made it safe for the first land-based life to migrate out of our oceans. Only 600 million years ago Earth’s atmosphere had built up enough ozone to shield life from the Sun’s lethal ultraviolet radiation. On Earth, photosynthesis over billions of years is responsible for our planet’s high oxygen levels and thick ozone layer. Although some ozone signatures had been detected in previous ground-based observations during lunar eclipses, Hubble’s study represents the strongest detection of the molecule to date because it can look at the ultraviolet light, which is absorbed by our atmosphere and does not reach the ground. The measurements detected the strong spectral fingerprint of ozone, a key prerequisite for the presence – and possible evolution – of life as we know it in an exo-Earth. It is for these reasons that Hubble is very rarely pointed at the Moon. Furthermore, the Moon is so close to Earth that Hubble had to try and keep a steady eye on one select region, to precisely track the Moon’s motion relative to the space observatory. These observations were particularly challenging because just before the eclipse the Moon is very bright, and its surface is not a perfect reflector since it’s mottled with bright and dark areas. Using a space telescope for eclipse observations is cleaner than ground-based studies because the data is not contaminated by looking through Earth’s atmosphere. Instead, astronomers used the Moon as a mirror that reflects the sunlight that has been filtered through Earth’s atmosphere. In a new study, Hubble did not look at Earth directly. 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. To prepare for exoplanet research with bigger telescopes that are currently in development, astronomers decided to conduct experiments much closer to home, on the only known inhabited terrestrial planet: Earth. This is the first time a total lunar eclipse was captured from a space telescope and the first time such an eclipse has been studied in ultraviolet wavelengths. This method serves as a proxy for how they will observe Earth-like planets around other stars in the search for life. Taking advantage of a total lunar eclipse, astronomers using the NASA/ESA Hubble Space Telescope have detected ozone in Earth’s atmosphere.
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