This Exoplanet Is Raining, With Water!

This Exoplanet Is Raining, With Water!

Credit: ESA/Hubble, M. Kornmesser

Tough it is 34 parsecs (110 light-years) from Earth in the constellation Leo, raining with water could mean it potentially hots life.

What happened?

K2-18 b lies in the ‘habitable zone’ around its star — the distance at which liquid water could exist, making extraterrestrial life possible in its hydrogen-rich atmosphere.

Ever since the discovery of the first exoplanet, astronomers have made steady progress towards finding and probing planets in the habitable zone of their host stars, where the conditions could be right for liquid water to form and life to sprawl. Results from the Kepler mission indicate that the occurrence rate of habitable-zone Earths and super-Earths may be as high as 5-20%. Despite this abundance, probing the conditions and atmospheric properties on any of these habitable-zone planets is extremely difficult and has remained elusive to date. Here, we report the detection of water vapor and the likely presence of liquid water clouds in the atmosphere of the 8.6 M⊕ habitable-zone planet K2-18b. With a 33 day orbit around a cool M3 dwarf, K2-18b receives virtually the same amount of total radiation from its host star (1441±80 W/m2) as the Earth receives from the Sun (1370 W/m2), making it a good candidate to host liquid water clouds. In this study we observed eight transits using HST/WFC3 in order to achieve the necessary sensitivity to detect water vapor. While the thick gaseous envelope of K2-18b means that it is not a true Earth analogue, our observations demonstrate that low-mass habitable-zone planets with the right conditions for liquid water are accessible with present-day telescopes.

But there is a catch…

One thing worth mentioning is that presence of water alone doesn’t necessary mean that the planet is habitable, one good example is our neighbor Venus - our Sun’s rays have stripped away much of the water even it once had water vapor.

For a planet lies this far (110 light-years), more data is needed before people can make further moves.

What’s next?

The next generation of space telescopes will be able to characterize atmospheres in more detailed way as they will carry much more advanced instruments. Among which one called James Webb Space Telescope (JWST) from NASA is planned to launch in 2021 and will collect more data for us; another called Atmospheric Remote-sensing Infrared Exoplanet Large (ARIEL) from ESA is expected to launch in 2028 and will observe 1,000 planets in detail to get a truly representative picture of what they are like.


- Benneke, B. et al. Water Vapor on the Habitable-Zone Exoplanet K2-18b

- ESA Science & Technology - ARIEL

- James Webb Space Telescope (WEBB/JWST) NASA

Please leave a comment if you have any questions. 😄


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