Scientists using the James Webb Space Telescope have detected a specific gas in the atmosphere of a distant “water world” that could indicate the presence of life. The planet, known as K2-18b, is more than twice the size of Earth and orbits a cool red dwarf star about 120 light-years away in the constellation Leo.
Researchers identified traces of dimethyl sulfide (DMS) in the planet’s atmosphere. On Earth, this molecule is only produced by life, primarily by phytoplankton in marine environments. While the discovery is significant, scientists caution that more data is needed to confirm the presence of the gas and its biological origins.
A World Covered in Water
K2-18b is classified as a “Hycean” planet, a term scientists use to describe a world with a hydrogen-rich atmosphere and a surface covered by liquid water oceans. The NASA-led study suggests that the planet sits within the habitable zone, which is the region around a star where temperatures are just right for liquid water to exist.
The James Webb Space Telescope (JWST) analyzed the starlight passing through the planet’s atmosphere as it moved in front of its sun. This process, called transmission spectroscopy, allows scientists to see the chemical “fingerprints” of different gases.
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” said Nikku Madhusudhan, a professor at the University of Cambridge and lead author of the study.
The Chemical Clues
In addition to the potential discovery of DMS, the telescope found high levels of methane and carbon dioxide. The presence of these carbon-bearing molecules, combined with a lack of ammonia, supports the theory that there is a liquid ocean underneath a hydrogen-rich atmosphere.
The discovery of DMS is particularly exciting for the scientific community because there are no known natural chemical processes on Earth that produce the gas without living organisms. However, the signal for DMS is faint compared to the signals for methane and carbon dioxide.
“The upcoming JWST observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18b at significant levels,” Madhusudhan explained in a NASA press release .
Key Challenges in the Search for Life
Despite the presence of water and chemical markers, K2-18b may not be a comfortable place for humans. The planet’s large size—8.6 times the mass of Earth—means its interior likely contains a large mantle of high-pressure ice, similar to Neptune.
Scientists are also considering the following challenges:
- Atmospheric Pressure:The hydrogen atmosphere could be too thick, creating a greenhouse effect that makes the ocean too hot for life.
- Star Activity:Red dwarf stars are often active and may blast their planets with harmful radiation.
- Signal Accuracy:Distinguishing between a biological signal and a false positive at such a great distance is extremely difficult.
“Although this kind of planet does not exist in our solar system, Hycean worlds are among the most common types of planets known in the galaxy so far,” said team member Subhajit Sarkar of Cardiff University.
What Comes Next?
The team intends to use the telescope for follow-up research to validate the DMS finding. If confirmed, it would shift the focus of astrobiology toward water-rich worlds that are larger than Earth. For decades, the search for extraterrestrial life focused primarily on smaller, rocky planets like Mars or the moons of Jupiter and Saturn.
This discovery represents a milestone in “exoplanetology.” It proves that the JWST has the sensitivity required to detect chemical signatures in the atmospheres of planets orbiting other stars. Even if K2-18b turns out to be lifeless, the ability to analyze its air so clearly is a major technical achievement for NASA and its international partners.
For more information on the mission and ongoing exoplanet research, you can visit the official James Webb Space Telescope site .
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