Space Telescope Science
The possibility of life on other worlds has fueled humankind's imagination for centuries. Over the past 20 years, the explosion of discoveries of planets orbiting other stars has sparked the search for worlds like Earth that could sustain life. Most of those candidates were found with other telescopes, including NASA's Kepler space observatory. NASA's Hubble Space Telescope has also made some unique contributions to the planet hunt. Astronomers used Hubble, for example, to make the first measurements of the atmospheric composition of extrasolar planets.
Now, astronomers have used Hubble to conduct the first search for atmospheres around temperate, Earth-sized planets beyond our solar system, uncovering clues that increase the chances of habitability on two exoplanets. They discovered that the exoplanets TRAPPIST-1b and TRAPPIST-1c, approximately 40 light-years away, are unlikely to have puffy, hydrogen-dominated atmospheres usually found on gaseous worlds. Those dense atmospheres act like a greenhouse, smothering any potential life. Observations from NASA's upcoming James Webb Space Telescope will help determine the full composition of these atmospheres and hunt for potential biosignatures, such as carbon dioxide and ozone, and methane.