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Water vapor detected in the atmosphere of a super-Earth

Artist's illustration of a planet 110 light-years from Earth.
Artist's illustration of K2-18b. Credit: ESA/Hubble, M. Kornmesser

Scientists have found water vapor in the atmosphere of a world about 8 times the mass of Earth.

Why it matters: While this isn't the "Earth 2.0" scientists have been hoping to find, the discovery does mark another step along the path toward finding a truly habitable world beyond our own.

  • "We have found water vapor in the atmospheres of gaseous planets before, and in the atmospheres of hot super-Earths, but this is the first time water vapor has been found in the atmosphere of a temperate super-Earth," NASA exoplanet researcher Jessie Christiansen told Axios via email.

Details: The planet, called K2-18b, orbits a star that's smaller and dimmer than the Sun and is located about 110 light-years from Earth, according to a new study detailing the finding in Nature Astronomy.

  • K2-18b orbits its star in what's known as the habitable zone, where researchers think that water can exist for extended periods of time on a world's surface.
  • The planet was discovered in 2015 by the Kepler Space Telescope, but for this study, the researchers used data gathered in 2016 and 2017 by the Hubble Space Telescope to investigate K2-18b's atmosphere in more detail.
  • Another study looking at K2-18b that has not yet been published suggests that the world could have a water cycle and perhaps even rain.

The catch: Even if scientists confirm that there is an abundance of liquid water on K2-18b, that doesn't necessarily mean that there's also life.

  • The planet's host star might be more active than our Sun, meaning that K2-18b could be bombarded with more radiation than the Earth, making it inhospitable to life as we know it.
  • Water is just one ingredient needed to make a habitable world, according to Christiansen, who is unaffiliated with the new study, so follow-up observations will be key if scientists hope to figure out if this planet could support life.

What's next: Telescopes, like the James Webb Space Telescope that is expected to launch in 2021, could help shed light on the habitability of K2-18b and others like it.

  • Future observatories will be able to collect detailed data on exoplanet atmospheres, but at the moment, researchers don't have the technology needed to be able to actually tell whether a planet in distant space is habitable or not.

Go deeper: We wouldn't know it if we found another Earth