Water found for first time in atmosphere of exoplanet

Sophisticated tools were able to detect water vapour on K2-18b an exoplanet located 110 light years away

Astronomers have made a very interesting discovery: For the first time, water vapor has been detected in the atmosphere of an exoplanet that lies in the habitable zone for its star. Using the transit method, K2-18b was found to have a size of 2.7 times Earth's diameter, and using the reflex velocity method a mass of 8.6 times Earth's mass. This is now the only known exoplanet that contains water and also temperatures that are within the range necessary for supporting life, making it a key discovery for future potential missions. Its orbital path is much tighter than the one Earth follows around our sun (out there, a year would be just 33 Earth days)-but this intimate distance means the planet is still within the red dwarf star's habitable zone, the life-friendly region where temperatures are conducive to liquid water. The planet, discovered by NASA's Kepler Space Telescope in 2015, also has a mass eight times greater than Earth's.

For the first time, scientists searching for extraterrestrial life have found an exoplanet (a planet outside our solar system) that has water. NASA's TESS mission is expected to detect hundreds more super-Earths in the coming years.

It's definitely the smallest and coolest planet that we've had a glimpse into the atmosphere of so far. On Tuesday, Benneke's team posted its own analysis of K2-18b on the preprint server arXiv, which hosts academic papers not yet published in peer-reviewed journals. It orbits a red dwarf star 110 light-years away from Earth in the Leo constellation. Signs of atmospheric water, oxygen and methane would all be signs that a planet may support life.

Hubble observations resulted in a distinct water signal, but the UCL researchers weren't certain about the amount of water packed into the atmosphere of K2-18b, or whether liquid water exists at the surface. The researchers said they clearly saw the signature for water vapor in the atmosphere when they put the data through algorithms. However, it brings us closer to answering the fundamental question: "Is the Earth unique?", Tsiaras said.

Though K2-18b is likely solid at its core, the temperatures and pressures at the "surface" would be so high that few complex molecules would survive, let alone any life forms. The habitable zones of red dwarves are close to the star for this reason, and the authors note that the equilibrium temperature on K2-18b could be quite similar to Earth's.

Graphic shows the approximate size of super Earth K2-18b compared to Earth and Jupiter
Water vapor has been spotted on a “habitable zone” planet 110 light years away

There's still a chance it could be bathed in a huge ocean, though, which would be more suitable for life, Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico, who was not involved in either study, told Daniel Oberhaus at WIRED.

So far, attempts to gauge the atmospheres of terrestrial super-Earths have failed, either because of thick clouds (as was the case for Gliese 1214 b and HD 97658 b), a lightweight, featureless atmosphere of just hydrogen and helium (as for 55 Cancri e), or no atmosphere and no clouds at all (as for six of the planets in the TRAPPIST-1 system).

Researchers must wait for more sophisticated tools, such as the long-delayed James Webb Space Telescope, to reveal more details about the distant world.

The lead scientist, Prof Giovanna Tinetti of University College London (UCL) described the discovery as "mind blowing".

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