A team of scientists has detected chemical signals on the alien planet K2-18 b that, on Earth, are only produced by biological processes. This finding, made with the James Webb Space Telescope, represents the strongest evidence yet of possible life beyond the solar system.

Evidence of life on an alien planet

The gases dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were detected in the atmosphere of K2-18 b. On Earth, both compounds are produced exclusively by living organisms, particularly by microbes such as marine phytoplankton.

These compounds were not only identified with a 99.7% statistical certainty but also found at surprisingly high concentrations—over 10 parts per million by volume. On our planet, such concentrations are thousands of times lower, suggesting possible biological activity.

Nikku Madhusudhan, an astrophysicist at the University of Cambridge, led the study. While he emphasizes that the existence of life cannot yet be confirmed, the data does represent a clear biosignature—a chemical footprint linked to biological processes.

K2-18 b, classified as a “sub-Neptune,” has a mass 8.6 times that of Earth and a diameter 2.6 times greater. It orbits within the habitable zone of a red dwarf star located 124 light-years away, in the constellation Leo.

The habitable zone is defined as the region where temperatures could allow for the presence of liquid water, considered essential for life as we know it. This alien planet gathers physical conditions that make it an ideal candidate for astrobiological research.

The Webb telescope, operational since 2022, has revolutionized astronomical observation. Its capabilities allow scientists to analyze the atmospheres of exoplanets with unprecedented precision, as in the case of K2-18 b, through the transit method.

A Hycean World: Warm Oceans and Microbial Life

AlIen planet K2-18 b could belong to a theoretical class of exoplanets called “hycean worlds,” characterized by hydrogen-rich atmospheres and warm oceans—environments potentially habitable for microbial life forms.

Madhusudhan suggests that if such worlds exist, they could harbor life forms similar to Earth’s marine microbes. The oceans of K2-18 b, possibly even warmer than those on Earth, may serve as breeding grounds for resilient unicellular organisms.

The term “hycean” merges “hydrogen” and “ocean,” evoking extreme but fertile environments for basic life forms. This type of planet offers a new avenue in the search for life beyond Earth.

Previous observations from the Webb telescope had already revealed the presence of methane and carbon dioxide in the alien planet atmosphere. Now, using different instruments and light wavelengths, scientists have confirmed the existence of even more specific biosignatures.

While some independent researchers have called for caution, the scientific community acknowledges that K2-18 b has become one of the most intriguing worlds known to date. Further observations will be essential to validate the findings.

The method used—known as transit spectroscopy—involves analyzing the light that passes through a planet’s atmosphere as it transits in front of its star. Each gas leaves a distinct fingerprint on that light, allowing researchers to determine its presence with high accuracy.

Even so, Madhusudhan notes that these results must be confirmed two or three more times before any definitive claims about life can be made. Only then can science reduce the margin of error to negligible levels.

In addition, scientists must investigate alternative non-biological explanations for the presence of DMS or DMDS. While no abiotic processes are currently known to produce them under such conditions, researchers remain cautious.

The discovery of biosignatures on K2-18 b marks a major breakthrough in the search for extraterrestrial life. Although further observations are needed to confirm a biological origin, the possibility that we are not alone now feels closer than ever.

Reference:

• ariXv/A Comprehensive Reanalysis of K2-18 b’s JWST NIRISS+NIRSpec Transmission Spectrum. Link.

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