Daniel Apai, Associate Dean for Research and Professor of Astronomy and Planetary Science at the University of Arizona. It was originally published in conversation.
A team of astronomers announced on April 16, 2025, that in the process of studying the planet around another star, they found evidence of unpaid atmospheric gases. On Earth, its gas – called dimethyl sulfide – is produced primarily by living tissue.
In April 2024, James Webbspace Telescope stared at the host star of planet K2-18B for nearly six hours. Meanwhile, the orbiting planet passed by the stars. Starlights were filed through the atmosphere and transported fingerprints of atmospheric molecules to the telescope.
JWST’s cameras can see the light that passes through its atmosphere and detect molecules in the planet’s atmosphere. European Space Agency
By comparison, by acquiring fingerprints to 20 molecules that can be observed in the atmosphere, astronomers have concluded that the most likely match is gas, a good indicator of life on Earth.
I am an astronomer and an astronomer studying planets around other stars and their atmospheres. In my job, I try to understand which nearby planets are suitable for life.
K2-18b enters the world of Misters
To understand what this discovery means, let’s start with the strange world in which it was discovered. The planet is named K2-18b. In other words, it is the first planet in the 18th Planet System discovered by the expanded NASA Kepler mission, K2. Astronomers assign the “B” label to the first planet in the system rather than the “A” to avoid positive confusion with the star.
The K2-18B is just over 120 light years from the Earth-to-Galaxy scale, and this world is practical in our backyards.
Astronomers know little about the K2-18B, but they know that unlike Earth, it is different. First, it is about 8 times larger than the Earth, and has a volume of about 18 times larger. This means it is roughly the same as Earth. In other words, it must have a large amount of water, but it is not too dense or even less of a big atmosphere.
Astronomers think that this world is either a small version of the giant Neptune of our solar system ice, known as the Mini Neptune, or a rocky planet, perhaps a waterless rocky planet.
Another option is that the planet is a “high cyan world,” as recently proposed by astronomer Nick Madusdan at the University of Cambridge.
Astronomers predict that the Hikia world is more frequent than the Earth’s oceans and breaks down the lack of continents many times, so the term means hydrogen over-ocean. These oceans are covered in large quantities of hydrogen atmospheres, tens of millions of heights.
Astronomers still don’t know that there is a certainty of Hycean world, but models of how they look are consistent with the limited data collected with the K2-18b and other telescopes.
This is where the story gets exciting. Mini Neptin and Gas Dwarves are unlikely to be friendly for life as they have no liquid water and have a large pressure on their inner surface. However, the planet of Hycean has a large, mild ocean. So, can the Hycean Worlds oceans be habitable?
DMS detection
In 2023, Madhusudhan and his colleagues inspected Starlight, which first met the atmosphere of the K2-18B using a James Webb Space Telescope short-wave infrared camera.
They found evidence of two simple carbon-containing molecular molecules carbon monoxide and methane, indicating that there is no water vapor in the upper atmosphere of the planet. This atmospheric composition did not supply the idea that the K2-18B could be the world of HYCEAN. In the Hycean world, water is trapped in the deeper ocean and warmer atmosphere than in the upper atmosphere probed by JWST observations.
Interestingly, the data also showed additional VRAY weak signals. The team discovered that this weak signal coincides with a gas called dimethyl sulfide (DMS). On Earth, DMS is produced in large quantities by seaweed. Even if there are non-biological sources, it has hardly changed.
This signal made early detection exciting. On planets that could have huge oceans, there is likely a gas issued by biological organisms on Earth.
K2-18b can have a deep ocean and hydrogen atmosphere that spans the planet. Amanda Smith, Nick Madhusdun (Cambridge University), CC BY-SA
Scientists have shown a complicated response to this first annemement. Although the findings were exciting, Suba Astronomers considered the observed DMS signal to be weak and the Hyceanity of K2-18b was uncertain.
To deal with it before the concert, Mashusudhan’s team returned the JWST to the K2-18B a year later. This time they used a different camera in JWST to look for light in a different range of wavelengths. New Results Published on April 16, 2025 – Supported the initial findings.
These new data show that the team is more powerful – but still weak – shows that it is still weak in Reativley, indicating that it is due to seeing DMS or similar molecules. The fact that DMS signals appeared on another camera during another set of observations has strengthened the interpretation of atmospheric DM.
Madhusudhan’s team presented VRY with a detailed analysis of data and interpretation uncertainty. In actual measurements there is always sub-uncertainty. They find that uncertainty is unlikely to explain the signal of the data and further support DMS interpretation. As an astronomer, and it finds an exciting analysis.
Is life there?
Does this mean that scientists have found life in another world? Perhaps – but we can’t be sure yet.
First of all, does K2-18B really have the ocean under the thick atmosphere? Astronomers need to test this.
Secondly, is the signal seen on a two-year camera really from dimethyl sulfide from two-year apal? Scientists certainly need more sensitive measurements and more observations of the planet’s atmosphere.
Third, if it’s actually DMS, does this mean there’s life? This may be a difficult question to answer. Life itself cannot be detected with existing technology. Astronomers need to assess and exclude all other potential options to build confidence in this possibility.
New measurements may lead researchers to historical discoveries. However, important uncertainty remains. Astrobiologists require a very decolorization of the world similar to the K2-18B before representatives of the DMS and their interpretations can be confident as a signature of life.
Scientists around the world are scrutinizing already published research, and independent verification is at the heart of science, so they are working on new tests of findings.
Moving forward, the K2-18B will become an inexplicable target for JWST, the world’s most sensitive telescope. JWST may observe other potential Hycean worlds to see if signals appear in the atmosphere of these planets.
With more data, these tentative conclusions may not stand the test of time. But for now, the prospect that astronomers may have detected gases released by alien ecostems foaming in the dark blue seas is a very attractive possibility.
The true nature of the K2-18B shows new results that use JWST to investigate other worlds to explore alien life cues, ensuring the following year is thrilling for astrobiologists.
