Huge news! Astronomers using the Hubble space telescope have discovered water in the atmosphere of an exoplanet in its star’s habitable zone. If confirmed, it will be the first time we’ve detected water—a critical ingredient for life as we know it—on an exoplanet. The water was detected as vapour in the atmosphere, but the temperature of the planet means it could sustain liquid water on its surface, if it’s rocky.

The planet is called K2-18b, and it’s about 110 light years away. The planet is much different than Earth. It’s a Super-Earth, and it’s twice as large as Earth, and about 8 times as massive. K2-18b is orbiting a red dwarf star, and it was first discovered in 2015 by the Kepler Space Telescope.

Dr. Angelos Tsiaras (UCL Centre for Space Exochemistry Data, CSED), said: “Finding water on a potentially habitable world other than Earth is incredibly exciting. K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?”

The team behind the discovery developed algorithms and ran archived Hubble data from 2016 and 2017 through them. They analyzed starlight from the red dwarf star as it passed through the exoplanet’s atmosphere. They discovered the molecular signature of water, as well as hydrogen and helium.

This discovery needs follow-up observations to confirm it. We also need better telescopes to study its atmosphere in greater detail, and the atmospheres of other exoplanets. Two telescopes on the horizon will tackle that job. The James Webb Space Telescope will have the powerful capability to examine the atmospheres of exoplanets, which is really the next step in understanding all of the exoplanets found by Kepler, and which will be found by TESS.

The ESA’s ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission will launch in 2028 and will study the atmospheres of about 1000 exoplanets in detail. ARIEL, along with the JWST, will give us a much better understanding of K2-12b and exoplanets like it.