NASA finds first super-Earth exoplanet with water vapor in habitable zone

Rodiano Bonacci
Settembre 13, 2019

About 110 light years from Earth, an exoplanet eight times the mass of Earth orbits a star.

There are other ingredients that are necessary too, and there are promising signs that K2-18b might harbor more than just water vapor.

So, while the presence of water vapor on K2-18b would probably not tell us anything about the habitability of that planet, it would indicate that water is likely to exist within the habitable zone of other stars, making any planets there worth careful observation.

K2-18b is one of hundreds of "super-Earths" - exoplanets with masses between those of Earth and Neptune - found by Kepler.

"With so many new super-Earths expected to be found over the next couple of decades, it is likely that this is the first discovery of many potentially habitable planets", said Ingo Waldmann, study co-author and lecturer in extrasolar planets at the University College London's Centre for Space Exochemistry Data. 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.

Because light from the K2-18b's star takes a century to reach the Earth, to travel over there would be "impossible", he said. Over 4,000 exoplanets have been detected but we don't know much about their composition and nature.

"The fact we can now make observations that allow us to work out what's in the atmosphere of a planet twice the Earth's radius, orbiting a star that is just over a quadrillion kilometres away, is just awesome", Horner said. Preliminary scans of the exoplanet suggested it was a super-Earth, that is, a rocky planet larger than Earth, and that it featured an atmosphere.

Björn Benneke (University of Montreal) led a team in applying for time on the Hubble Space Telescope, observing the planet as it crossed the face of its star.

In a tantalizing first, scientists have discovered water at a planet outside our solar system that has temperatures suitable for life. The researchers said they clearly saw the signature for water vapor in the atmosphere when they put the data through algorithms. 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. Our results have been published in Nature Astronomy. However, it brings us closer to answering the fundamental question: "Is the Earth unique?", Tsiaras said. Although there are many other criteria for habitability, such as the presence of oxygen in the atmosphere, our research has made K2-18b the best candidate to date.

But the more important aspect of all this is that these observations show that finding water vapor in the atmospheres of temperate planets is possible.

The researchers also want to estimate cloud coverage and the amount of atmospheric water on the planet. At the same time, however, the new findings could represent a blow to the planet's potential to foster life, said Louden, who's not affiliated with the new research. If that's true, K2-18b would be the first known exoplanet with clouds of water vapor, Greshko reports.

The next generation of space telescopes, including the European Space Agency's ARIEL mission, will be able to observe atmospheres in more detail.

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