A distant super-Earth in space hosts a vast alien ocean but shows no signs of life, say scientists

K2-18 b is a super Earth exoplanet that orbits an M-type star. Its mass is 8.92 Earths, it takes 32.9 days to complete one orbit of its star, and is 0.1429 AU from its star. (Image: NASA)

In deep space, 124 light-years away, a planet called K2-18 b had sparked the hopes of many. Scientists thought they saw hints of life or at least, the building blocks of it. But after fresh eyes and better data, those early whispers of biology have faded.

K2-18 b orbits a red dwarf star and is much larger than Earth. It’s known as a sub-Neptune planet, which means it’s rich in gas but not as big as Jupiter. Earlier this year, scientists studying telescope data thought they had spotted dimethyl sulphide and dimethyl disulphide molecules on Earth made only by life. That idea quickly caused debate, as other experts couldn’t find the same result.

Now, a fresh group of scientists has looked again, using new data from four more James Webb Space Telescope transits. Their findings, posted recently on the arXiv server, paint a clearer but more sobering picture.

Water, but no signs of life
The team confirmed a strong presence of methane and carbon dioxide in the planet’s atmosphere. But they found no trace of the suspected life-linked molecules. In fact, they also found no water vapour, which puzzled some researchers. The absence could mean water vapour gets trapped lower down and doesn’t reach the higher layers their tools can study.

Still, there’s little doubt the planet is filled with water in some form. Either it has a deep atmosphere filled with vapour or hides a liquid ocean beneath a thinner shell of gas. Both cases suggest a water-rich planet, though not one with clear signs of life.

Cold, deep and far from Earth-like
There was no sign of ammonia or carbon monoxide either. That fits with theories about a cold ocean, but nothing can be said for sure. More data is needed, especially to study how carbon gases behave on this planet.

The study’s authors note that K2-18 b is still worth watching. It’s not Earth-like, but it is cool and filled with water, which is something rare in space studies. The planet now stands as one of the most promising places to study oceans beyond Earth, even if they are lifeless.

For now, the cosmic mystery continues. Not all clues point to life, but every answer helps us understand what else is out there.