Astronomers find evidence of extraterrestrial life on exoplanet K2-18b of Hycean worlds

A team of astronomers from the University of Cambridge announced the discovery of one of the most promising signs of potential extraterrestrial life. Researchers found molecules in the atmosphere of exoplanet K2-18b that, like on Earth, are produced by living organisms.

Photo: commons.wikimedia.org by Detlef Hartmann, https://creativecommons.org/publicdomain/zero/1.0/

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The discovery has caused a sensation and has already been called "the strongest evidence yet” of life beyond the Solar System.

Exoplanet K2-18b, located in the constellation Leo, orbits its star at a distance of 124 light-years from Earth.

With the help of the James Webb Space Telescope (JWST), the astronomers could detect chemical traces of substances — methane and carbon dioxide — associated with the presence of life.

According to the scientist, the concentration of these molecules in the planet's atmosphere is thousands of times higher than on Earth.

If life is confirmed on K2-18b, it would suggest that life is widespread throughout the galaxy.

The planet may have a hydrogen-rich atmosphere and deepest ocean

Mans Holmberg, co-author of the study and researcher at the Space Telescope Science Institute, told The Washington Post that the observations suggest the planet has a hydrogen-rich atmosphere and an ocean deeper than any of the oceans we have on our planet Earth.

Scientists urge caution in claiming extraterrestrial life

The scientific community acknowledged the potential importance of the discovery. Yet, it is premature to make bold statements. 

Researchers plan to conduct further observations of K2-18b using the same telescope to confirm or refute the presence of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in its atmosphere. These are highly reactive gases, meaning if they are present, something must be constantly producing them as part of potentially biological processes.

While current measurements already show fairly high concentrations of these compounds, scientists stress that more data is needed.

K2-18b's temperature close to Earth's

Discovered in 2015, K2-18b is about 2.6 times larger and 8.6 times more massive than Earth. Its temperature is very similar to Earth's, but the planet orbits so quickly that a year on K2-18b lasts just 33 days. Many experts believe it is covered by the ocean and belongs to the so-called Hycean worlds — planets with a hydrogen-rich atmosphere and vast water coverage.

Water was first detected on K2-18b in 2019. Astronomer Angelos Tsiaras and colleagues identified water vapor in its atmosphere, and conditions that allow for the presence of liquid water. Leading researcher Björn Benneke noted the possibility of heavy rainfall on the planet, calling it one of the most exciting conclusions.

In 2020, scientists suggested K2-18b may contain a water ocean and could be habitable. The planet orbits in the habitable zone around a red dwarf star — that is, at a distance where life could potentially exist.

Details

An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such until 2016. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detected in 1988, was confirmed in 2003. As of 26 March 2025, there are 5,867 confirmed exoplanets in 4,377 planetary systems, with 985 systems having more than one planet. In collaboration with ground-based and other space-based observatories the James Webb Space Telescope (JWST) is expected to give more insight into exoplanet traits, such as their composition, environmental conditions, and potential for life.