NASA says exoplanet K2-18 b could be ocean world, or ‘Hycean’ planet

Scientists have made a new discovery that hints at a possible water ocean on a massive planet many lights-years away from Earth, though it is not clear if it could support life, according to NASA.

Researchers made the announcement after examining data from NASA’s James Webb Space Telescope, gazing more than 100 light-years from Earth at an exoplanet — or a planet beyond our solar system — in the constellation Leo that goes by the name K2-18 b and is 8.6 times as massive as our planet.

The astronomers, led by the University of Cambridge, found methane and carbon dioxide in the atmosphere of K2-18 b, results that are “consistent with an ocean-covered surface underneath a hydrogen-rich atmosphere,” the university said.

“The discovery provides a glimpse into a planet unlike anything else in our Solar System, and raises interesting prospects about potentially habitable worlds elsewhere in the Universe,” it said Monday.

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NASA said the findings — including “the abundance of methane and carbon dioxide, and shortage of ammonia” — support the hypothesis that the exoplanet might be covered in ocean.

The researchers said they also detected “another, weaker, signal” that could indicate the molecule called dimethyl sulfide, raising the prospect of biological activity on K2-18 b. On Earth, this molecule is only produced by life, emitted from phytoplankton in marine environments, NASA says.

But the DMS detection is yet to be confirmed, and the team will follow up with further observations from the Webb telescope, the U.S. space agency added.

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The astronomers noted that their findings did not necessarily mean the planet could support life: Its large size means its interior could contain a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface, they said. And the ocean might be too hot to be habitable.

It’s not the first time astronomers have seen signs of water on other planets. Evidence of water vapor has previously been found on an exoplanet roughly the size of Neptune about 120 light-years away.

Still, they described the new revelations as a gateway to more insight on planets beyond Earth.

NASA said the prospect that K2-18 b could be a “Hycean” exoplanet, or an ocean world, was “intriguing,” as some astronomers believe such planets are promising environments to search for evidence of life on exoplanets.

“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” said astrophysicist Nikku Madhusudhan of Cambridge’s Institute of Astronomy, the lead author of the study.

K2-18 b, more than twice as large as Earth, was discovered in 2015 sitting in its star’s “habitable zone,” a range that is neither too hot nor too cold to host liquid water.

The first insight into the planet’s atmospheric properties came from NASA’s Hubble Space Telescope, but the technology of its successor, the Webb telescope, including extended wavelength range and “unprecedented sensitivity,” have made the latest detections possible, Madhusudhan said.

The $10 billion Webb telescope has peered deeper into space and delivered new observations of faraway galaxies since its launch in December 2021.

“These results are the product of just two observations of K2-18 b, with many more on the way,” said co-author and researcher Savvas Constantinou of the University of Cambridge.


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