Life Beyond Earth? Strong Biosignature Hints Detected on Exoplanet K2-18b

Shubham Kumar
Apr 21
3 min read

Spaceship orbiting a green and brown planet in space, partially illuminated. Dark, starry background. Peaceful and vast atmosphere. — Artistic impression of exoplanet K2-18b

For decades, astronomers and astrobiologists have scanned the skies, searching for signs that life may exist beyond the Earth. Now, new findings from the James Webb Space Telescope (JWST) have delivered one of the most tantalising clues yet: potential biosignatures in the atmosphere of exoplanet K2-18b, suggesting that alien life—possibly microbial—might be thriving outside our solar system.

🔭 What Did Astronomers Discover?

A team of researchers led by Professor Nikku Madhusudhan from the University of Cambridge has announced the detection of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) in the atmosphere of the distant exoplanet K2-18b. These chemical compounds are incredibly significant. On Earth, DMS is produced exclusively by biological organisms, primarily marine phytoplankton. There is no known abiotic process on Earth that produces DMS in significant quantities.

Scuba diver swims over vibrant coral reef, surrounded by colorful fish in clear blue ocean water. Bright and serene underwater scene.

The presence of DMS and DMDS in K2-18b’s atmosphere therefore suggests the possibility of biological processes occurring there—or, at the very least, unknown chemical pathways we have yet to understand.

🌍 What Is K2-18b?

K2-18b is an exoplanet located about 124 light-years away in the constellation Leo. It orbits a red dwarf star within the habitable zone, the region where conditions might allow for liquid water to exist. The planet is classified as a Hycean world, a newly proposed category of potentially habitable exoplanets characterized by deep oceans beneath a hydrogen-rich atmosphere.

A colorful planet with swirling green and yellow patterns set against a dark starry sky, evoking a sense of mystery and wonder. — exoplanet K2-18b

K2-18b is about 8.6 times the mass of Earth and 2.6 times its size—making it a “mini-Neptune” in terms of scale. Its thick atmosphere and potential for surface oceans make it an exciting target in the search for extraterrestrial life.

💡 Why Is the Detection Important?

This detection isn’t just a speculative guess—it’s grounded in solid astrophysical data. The findings have reached three-sigma statistical significance, which means there’s only a 0.3% chance that the signal is a fluke. While this doesn't meet the stringent five-sigma threshold needed to declare a scientific discovery, it strongly suggests the presence of these molecules.

The team estimates they need 16 to 24 more hours of JWST observations to achieve that five-sigma confidence.

The breakthrough came using JWST’s Mid-Infrared Instrument (MIRI), which analysed the planet’s atmosphere in a wavelength range that did not overlap with previous observations. This independent validation using a different instrument and part of the electromagnetic spectrum adds weight to the discovery.

🧪 How Are These Molecules Detected?

When K2-18b passes in front of its star from our vantage point (a transit), starlight filters through the planet’s atmosphere. Certain wavelengths of light are absorbed by molecules in the atmosphere, leaving unique imprints in the light that reaches JWST.

By studying these absorption lines, scientists can identify the gases present in the exoplanet’s atmosphere.

Earlier observations using JWST’s NIRISS and NIRSpec instruments detected methane (CH₄) and carbon dioxide (CO₂) in K2-18b’s atmosphere—both carbon-based molecules that further fuel the idea that the planet could host life.

The most recent detection of DMS and/or DMDS provides a new line of evidence and potentially a smoking gun biosignature.

🌊 What Are Hycean Planets?

Hycean planets are a class of worlds proposed by Professor Madhusudhan in 2021. They are characterized by:

Deep oceans beneath a thick hydrogen-rich atmosphere
Warm, potentially habitable surface environments
Large radii and masses compared to Earth

These planets, previously thought too large to be habitable, could actually offer more stable environments for life to develop. The detection of carbon-based molecules and now possible biosignatures in a Hycean atmosphere like K2-18b's suggests this class of planets might be more habitable than once thought.

Rocky planet with a textured surface floats in space. A distant red star glows brightly in the starry background. No text visible.

🧬 Could This Be Life?

While the presence of DMS and DMDS is deeply intriguing, caution is essential. There’s still a chance that non-biological processes—perhaps unknown to us—could be responsible for their formation. However, on Earth, DMS is exclusively produced by living organisms, especially plankton in the oceans, making it one of the more reliable biosignature candidates.

If confirmed, this would be the first time life’s chemical signature has been detected outside the solar system, potentially transforming our understanding of biology and the cosmos.

🔍 What’s Next?

Astronomers are now pushing for more observation time with JWST to further refine their data. If they can reach the five-sigma mark, we could be looking at the first confirmed detection of alien life—or at least alien biochemistry.

Regardless of the final outcome, this discovery represents a monumental leap forward. It demonstrates how next-gen space telescopes like JWST are revolutionizing our ability to study exoplanets and search for life across the galaxy.