A distant planet has water vapor

Abstract

For the first time, two groups of scientists have identified water vapor in the atmosphere of a distant planet not much bigger than Earth. Scientists think the planet, known as K2-18b, is about nine times as massive as Earth and twice its diameter. It’s the right distance from its star to be habitable but probably looks more like gaseous Neptune than rocky Earth. Water vapor has been detected on exoplanets before, but only on larger, hotter gas giants. Using the Hubble Space Telescope, a team led by Bjorn Benneke of the University of Montreal captured images of the planet as it passed in front of the red dwarf star it orbits 110 light-years from Earth. Independently, Benneke’s group and Angelos Tsiaras, Ingo P. Waldmann, and colleagues at University College London used computer programs to analyze light from the star as it passed through the planet’s atmosphere and deduce the atmospheric