Is There Life on Exoplanet K2-18b? Exciting New Results

K2-18b is an exoplanet 124 light years away and has a mass larger than Earth. Scientists say it may be entirely ocean-like, deep beneath its hydrogen atmosphere. Could that environment support life?

1. New observations from the Webb Space Telescope show that there is a molecule called dimethyl sulfide in its atmosphere, a possible sign of life. Webb had detected it before, but the new observations show a stronger signal.
2. The results do not prove that there is life on K2-18b, but they are intriguing. However, other scientists are quite skeptical about the study's conclusions.

Is there life on exoplanet K2-18b?

In 2023, scientists announced that they had detected dimethyl sulfide gas — a biosignature of life — in the atmosphere of K2-18b , an exoplanet 124 light-years away. On April 17, 2025, scientists at the University of Cambridge in the United Kingdom said they had found the gas again using the Webb Space Telescope, but this time the signal was stronger. They said dimethyl sulfide appears to be thousands of times more abundant on K2-18b than on Earth. However, more data is needed to fully confirm its presence and whether it is related to life.

What does dimethyl sulfide gas tell us?

K2-18b is a super-Earth or sub-Neptunian world, orbiting in the habitable zone – where liquid water could exist. The exact classification of the planet remains a matter of debate among scientists, which has had a major impact on the reported discovery. It is 2.6 times larger than Earth, and orbits a red dwarf star about 124 light years away.

When scientists announced the discovery of dimethyl sulfide (DMS) in September 2023 using the Webb Space Telescope, the news sparked a lot of discussion. It was certainly a potentially exciting discovery. The gas was a potential biosignature, a chemical, molecular, or other trace of biological life. But the detection was weak, so it wasn't conclusive. Astronomers would need to observe the planet again with Webb to try to determine whether the gas was really there.

Nikku Madhusudhan, an astrophysicist at the University of Cambridge, was involved in the previous research and is the lead author of the paper on the latest findings. He said:

We don't know for sure if the signal we saw last time was due to dimethyl sulfide, but just the hint of it was interesting enough that we looked again through Webb with another device.

Webb has previously detected methane and carbon dioxide in K2-18b's atmosphere. However, those signals were much stronger and have been confirmed. The dimethyl sulfide signal is weaker, or of "low statistical significance," in scientific jargon.

Is dimethyl sulfide more abundant on Earth than on K2-18b?

One big surprise from the results was the apparent amount of dimethyl sulfide in the planet's atmosphere. If the results are accurate—which has yet to be confirmed—then K2-18b has thousands of times more dimethyl sulfide in its atmosphere than Earth. On Earth, the amount is less than one part per billion. But on K2-18b, the amount of dimethyl sulfide is estimated to be 10 parts per million.

New observations have revealed the transient existence of a gas similar to dimethyl disulfide. Both molecules belong to the same chemical family and could be potential biomarkers.

On Earth, marine organisms like plankton produce most of the dimethyl sulfide. But it can also form without life and has been detected in comets and gas clouds in space. So its presence is not a sure sign of life. At least not yet.

Marvin Fry

Update 25 May 2025