With data from the Hubble Space Telescope, water vapor has been detected in the atmosphere of an exoplanet within the habitable zone of its host star. K2-18b, which is eight times the mass of Earth, is the only planet orbiting a star outside the solar system (or “exoplanet”) known to have both water and temperatures that could support life.
Credits: NASA's Goddard Space Flight Center
The authors of the paper, published in Nature Astronomy, believe that other molecules, including nitrogen and methane, may be present but they remain undetectable with current observations. Further studies are required to estimate cloud coverage and the percentage of atmospheric water present. A paper from a different team of scientists using Hubble observations has been submitted to the Astronomical Journal.
K2-18b is one of hundreds of "super-Earths" — exoplanets with masses between those of Earth and Neptune — found by Kepler. NASA’s TESS mission is expected to detect hundreds more super-Earths in the coming years. The next generation of space telescopes, including the James Webb Space Telescope, will be able to characterize exoplanet atmospheres in more detail.
The Hubble Space Telescope is a project of international cooperation between ESA (the European Space Agency) and NASA.

Media Contact: Claire Andreoli, NASA's Goddard Space Flight Center, Greenbelt, Md.
Last Updated: Sept. 12, 2019
Editor: Rob Garner