by On April 16, 2025, a team of astronomers announced that in the process of studying a planet, they had found evidence of an unexpected atmospheric gas. On earth, this gas – dimethyl sulfide – is mainly generated by living organisms.
In April 2024, the James Webb Space Telescope stared at the host of the planet K2-18B for almost six hours. During this time, the surrounding planet went in front of the star. Star light filtered through its atmosphere and promoted the fingerprints of atmospheric molecules to the telescope.
By comparing these fingerprints with 20 different molecules, which you might observe in the atmosphere, the astronomers came to the conclusion that the most likely match was a gas that is a good indicator of life on Earth.
I am an astronomer and astrobiologist who studies planets for other stars and their atmospheres. In my work I try to understand which nearby planets are suitable for life.
K2-18b, a mysterious world
To understand what this discovery means, we start with the bizarre world in which it was found. The name of the planet is K2-18b, which means that it is the first planet of the 18th planetary system found by the extended NASA Kepler mission, K2. Astronomers assign the Babel “B” to the first planet in the system, not “A”, to avoid a possible confusion with the star.
K2-18B is just more than 120 light years from the earth-in galactic level this world is practically in our garden.
Although astronomers know very little about K2-18B, we know that it is very unlike. At the beginning it is about eight times more massive than the earth, and it has a volume that is about 18 times larger. This means that it is only about half as tight as the earth. In other words, it has to have a lot of water, which is not very dense or a very large atmosphere, which is even less dense.
Astronomers believe that this world could either be a smaller version of the ice giant Neptune of our solar system, a mini-new or maybe a rocky planet without water, but a massive hydrogen atmosphere, as a gas dwarf.
Another option, as the astronomer of the University of Cambridge Nikku Madhusudhan recently proposed, is that the planet is a “Hycean world”.
This term means hydrogen-over-ocean, since astronomers predict that hycean-worlds are planets with global oceans that are many times deeper than the earth and without continents. These oceans are covered by solid hydrogen atmospheres that are thousands of miles high.
Astronomers do not yet know that hycean worlds exist, but models for matching the limited data. JWST and other telescopes have collected on K2-18B.
Here the story becomes exciting. It is unlikely that mini-neptune and gas dwarfs are hospitable for life, since they probably do not have liquid water and their inner surfaces have enormous pressure. But a Hycean Planet would have a large and probably moderate ocean. Could the oceans of the Hycean worlds be habitable – or even inhabited?
Recognize dms
In 2023, Madhusudhan and his colleagues used the short-wave length infrared camera of the James Webb Space Telescope to inspect Starlight, which was filtered for the first time by the atmosphere of K2-18B.
They found indications of the presence of two simple carbon-containing molecular carbon monoxide and methane and methane and showed that the upper atmosphere of the planet was missing. However, this atmospheric composition did not prove that K2-18B could be a Hycean world. In a Hycean world, water in the deeper and warmer atmosphere would be trapped, closer to the oceans than the upper atmosphere, which was examined by JWST observations.
Interestingly, the data also showed an additional, very weak signal. The team found that this weak signal matched a gas with the name dimethyl sulfide or DMS. On earth, DMS is produced in large quantities by seaweed. It has very few, if at all, not biological sources.
This signal made the initial detection exciting: on a planet that has a massive ocean, there is probably a gas that is emitted on the ground of biological organisms.
Scientists had a mixed reaction to this first announcement. While the results were exciting, some astronomers pointed out that the DMS signal was weak and that the Hycean nature of K2-18B is very uncertain.
In order to clear up these concerns, the Mashusudhan team turned back to K2-18B a year later. This time they used another camera on JWST that is looking for another wavelength range. The new results announced on April 16, 2025 supported their first results.
These new data show a stronger, but still relatively weak signal that the DMS team or a very similar molecule ascribes. The fact that the DMS signal appeared on another camera during another sentence of observations made the interpretation of DMS stronger in the atmosphere.
The Madhusudhan team also presented a very detailed analysis of the uncertainties in the data and interpretation. There are always some uncertainties for real measurements. They found that these uncertainties probably do not take into account the signal in the data, which further supports the DMS interpretation. As an astronomer, I find this analysis exciting.
Is life out there?
Does this mean that scientists have found life in another world? Maybe – but we still can’t be sure.
Does K2-18b really have an ocean deep below its thick atmosphere? Astronomers should test this.
Second, is the signal that is two years from dimethyl sulfide in two cameras? Scientists need more sensitive measurements and more observations in the planet’s atmosphere in order to be safe.
Third, this means that if it is actually DMS, is there life? This can be the most difficult question. Life itself is not detectable with existing technology. Astronomers must evaluate and exclude all other potential options in order to build their trust in this opportunity.
The new measurements can lead researchers to a historical discovery. However, there are important uncertainties. Astrobiologists will need a much deeper understanding of K2-18b and similar worlds before they can convince themselves of DMS and its interpretation as a signature of life.
Scientists around the world are already examining the published study and will work on new tests of the results because the independent review is the focus of science.
K2-18B will be an important goal for JWST, the most sensitive telescope in the world. JWST could soon observe other potential Hycean worlds to determine whether the signal also appears in the atmospheres of these planets.
With further data, these preliminary conclusions may not be the test of the time. But for the time being, only the view is that astronomers have discovered gases that have been emitted by an alien ecosystem that is used up in a dark, blue -colored extraterrestrial ocean, an incredibly fascinating option.
Regardless of the true nature of K2-18B, the new results, such as the use of the JWST to examine other worlds for references to foreign life, guarantee that the next few years will be exciting for astrobiologists.
This article will be released from the conversation, a non -profit, independent news organization that brings you facts and trustworthy analyzes to help you understand our complex world. It was written by: Daniel Apai, University of Arizona
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Daniel Apai receives financing for astrobiology research from NASA, the Heising Simons Foundation and the Gordon and the Betty Moore Foundation.
