Greek lead astronomer finds water on exoplanet twice the size of Earth

Pablo Tucker
September 13, 2019

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

The detection of water vapor in the atmosphere of this exoplanet is particularly exciting to the researchers because the exoplanet also lies within the habitable zone of its star, which includes the right temperatures for liquid water to exist on the surface of the planet and potentially support life as we understand it. The exoplanet could be a potential super-Earth (a planet with mass lesser than the masses of ten Earths), hinting at the probability of life outside the solar system.

A handout artist's impression released on September 11, 2019, by ESA/Hubble shows the K2-18b super-Earth, the only super-Earth exoplanet known to host both water and temperatures that could support life.

The team used data from NASA's Hubble Space Telescope to find water vapour in the atmosphere of K2-18b, by analysing starlight filtered through the exoplanet's atmosphere.


"K2-18b is not "Earth 2.0", he said.

Furthermore, it is argued that K2-18b is more of a super-Neptune than a super-Earth as its characteristics are reminiscent of Neptune than Earth. And now, water vapor has been detected in the atmosphere of a potentially habitable exoplanet for the first time. It's rocky and Earth-like, measuring 2.25 times wider and eight times more massive than our home planet.

This is the first time that scientists have found water in the atmosphere around a super-Earth. 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. Its star, a red dwarf, is considerably smaller and cooler than our sun, a yellow dwarf, and its atmosphere is also different than ours. What they saw is intriguing: They found evidence of water vapor in the planet's atmosphere.

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. However, it brings us closer to answering the fundamental question: "Is the Earth unique?" study first author Dr Angelos Tsiaras said in a statement issued by UCL. The researchers said they clearly saw the signature for water vapor in the atmosphere when they put the data through algorithms.


Ingo Waldmann, who is also a coauthor of the study and a physics lecturer at UCL, believes that there will be many other super-Earth exoplanets lying in habitable zones - that may contain water - waiting to be discovered in the future.

Aside from the tremendous distance separating Earth from K2-18b, the exoplanet is likely exposed to far more radiation than Earth, diminishing the prospects for life evolving there.

That's largely because the researchers are taking a transmission spectrum of the planet as it passes in front of its host star - that is, they're looking at the star's light as it passes through a thin sliver of the planet's atmosphere.

The University College London report describes the conditions on the planet known as K2-18 b. Further observations are needed to determine whether the planet is indeed a true water world, using next-generation observatories like NASA's James Webb Space Telescope and the European Space Agency's Ariel, both due to launch in the 2020s.


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