Hubble watched a lunar eclipse to see Earth from an alien’s perspective
To practice searching for extraterrestrial life, researchers have run a dress rehearsal with the one world they know to be habitable: Earth. While Earth was between the sun and moon for a lunar eclipse in January 2019, the Hubble Space Telescope observed how chemicals in Earth’s atmosphere blocked certain wavelengths of sunlight from reaching the moon. That observing setup mimicked the way astronomers plan to probe the atmospheres of Earthlike exoplanets as they pass in front of their stars, filtering out some starlight. “We basically pretend we’re alien observers looking at our planet,” says Giada Arney, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Using Hubble, the researchers focused on spotting the effects of atmospheric ozone. Because ozone is both a chemical by-product of oxygen produced in photosynthesis and a shield that protects life from the sun’s harmful ultraviolet rays, astronomers think atmospheric ozone could be a key indicator...