A research team led by Dr Nikku Madhusudan, an astrophysicist at the University of Cambridge, has found potential biosignatures in the atmosphere of a super Earth exoplanet K2-18b, located about 120–124 light-years from the Earth. K2-18b is considered to be a Hycean planet in the constellation Leo orbiting a red dwarf star. These recent observations made by using the James Webb Space Telescope (JWST) are published in the Astrophysical Journal of Letters.
Madhusudan has been a key figure in exoplanetary science, particularly in studying Hycean worlds—a term he coined to describe planets with hydrogen-rich atmospheres and global oceans, which are key elements of life. These planets are often larger and hotter than Earth, with some being up to 2.6 times the size of our planet and reaching atmospheric temperatures as high as 200 degrees Celsius (392 degrees Fahrenheit). His team’s findings suggest that K2-18b might be an ocean-covered world, potentially teeming with life, though further observations are needed to confirm this.
Role of the James Webb Space Telescope (JWST)
JWST 6.5 metre segmented mirror is capable of capturing distant cosmic light, revealing details that were previously hidden. Positioned 1.5 million km away from Earth at the second Lagrange (L2) point, it operates far from Earth’s interference, shielded by its five-layer sunshield, which keeps its instruments cool for optimal infrared detection.
Since its launch on December 25, 2021, the telescope revolutionised astronomy, providing breathtaking images of distant galaxies and analysing exoplanet atmospheres, detecting elements like carbon dioxide and water, which are crucial for understanding habitability beyond Earth.
What is a Biosignature?
NASA defines a biosignature as any characteristic, element, substance, or feature that can be used as evidence for past or present life. It must also be something that cannot be made without the presence of life. This can include things like a leaf or a feather, footprints in the mud, fossils stored away in the rocks, organic molecules made by life, or even differences in the chemistry of an atmosphere or a body of water.
Discovery of K2-18b
Astronomers first discovered K2-18b in 2015, using data from the Kepler Space Telescope. The planet was named K2-18b, indicating that it is the first planet discovered in the 18th system identified by NASA’s extended Kepler Mission, K2. Astronomers use the letter ‘b’ for the first planet in a system, rather than ‘a’, to prevent confusion with the name of the star.
The planet is about eight times the mass of Earth and orbits a red dwarf star, in the constellation Leo, that is smaller and cooler than our Sun. Importantly, K2-18b is located in the ‘habitable zone’ or Goldilocks Zone, the area around a star where liquid water could exist.
In 2019, data from the Hubble Telescope revealed some signs of water vapour in K2-18b’s atmosphere. In 2023, Madhusudan and his team used the short wavelength infrared camera of JWST to analyse the starlight passing through K2-18b’s atmosphere for the first time.
The team detected two simple carbon-based molecules in K2-18b’s atmosphere, carbon monoxide and methane. However, they found little to no water vapour in the planet’s upper atmosphere. This composition supports, but does not confirm, the theory that K2-18b might be a Hycean world, as in such a world, water would be located deeper in the atmosphere, near the oceans, rather than in the upper layers observed by the JWST.
Presence of Biosignatures
The data further revealed very faint signals matching with dimethyl sulphide (DMS) gas. On Earth, DMS is mainly produced by marine algae and has few, if any, non-biological sources. Scientists reacted with mixed responses to this announcement. The team also reported the possible detection of dimethyl disulphide (DMDS) gases, known to be produced by living organisms on Earth.
To address these concerns, Madhusudan’s team pointed the JWST at K2-18b once again. This time, they used a different camera on the telescope that observes a different range of light wavelengths. The new results, announced in April 2025, backed the team’s earlier findings.
The new data revealed a stronger—though still fairly weak—signal that the team links to DMS or closely-related molecules. The fact that this signal appeared again—using a different camera and during a separate observation—adds weight to the idea that DMS might be present in K2-18b’s atmosphere.
The reported detection of DMS or DMDS is intriguing but far from conclusive. The data could not clearly tell the two molecules apart, as they have nearly identical infrared signatures, making them look almost the same to the instruments. The signal is still so weak that false positives or equipment-related errors cannot be ruled out.
Limitations and Future Directions
Another major limitation is the lack of key information about the planet itself. Without a clear understanding of K2-18b’s environment, it is hard to interpret the findings accurately. Some studies even question whether the planet has a surface, any water or if it might be completely barren.
Madhusudan’s team also provided a detailed analysis of the uncertainties involved in their data and interpretations. However, they concluded that these uncertainties are unlikely to explain the signal, which strengthens the case of DMS.
The team is planning follow-up research using the telescope’s Mid-Infrared Instrument (MIRI) spectrograph, hoping to further confirm their findings and gain new insights into K2-18b’s environmental conditions.
Despite the uncertainty around the possibility of life, this study achieves something significant. It introduces a bold methodology that stretches the limits of what current technology could do in exoplanet research. More importantly, it lays out a clear path for what needs to happen next to either confirm or challenge its conclusions.
For instance, the study suggests that the amount of DMS or DMDS in K2-18b’s atmosphere is hard to explain without biological sources. This claim now invites further research to explore whether non-living processes could actually produce these gasses. To their credit, the authors themselves call for a ‘dedicated community effort’ to research further. But until they could confidently rule out abiotic sources, it is too soon to claim that these molecules are signs of life on K2-18b.
Future missions, such as the Nancy Grace Space Telescope, along with enhanced ground-based observatories, will play a crucial role in conforming these findings. Scientists also plan to use next-generation telescopes to analyse similar Hycean Worlds to determine whether K2-18b is an anomaly or part of a larger pattern among exoplanets.
Implications for the Future of Space Exploration
If follow-up studies confirm the presence of DMS and other life-related markers, this discovery could redefine our understanding of biology beyond Earth. The idea that life could exist in radically different conditions—such as within the hydrogen-rich oceans of Hycean worlds—would challenge conventional assumptions about habitability.
While scientists remain cautiously optimistic, the discovery on K2-18b represents one of the most compelling leads in the search for alien life. If proven true, it would mark one of the most profound moments in human history—a confirmation that we are not alone in the universe.
K2-18b’s discovery may reshape priorities in space exploration, with more focus on searching for biosignatures within hydrogen-dominated atmospheres rather than solely looking for planets with Earth-like conditions. It could influence future missions, such as next-generation telescopes, spacecraft designed for direct atmospheric sampling, and even proposals for robotic probes to distant exoplanets.
As technology continues to advance, the next few decades might finally provide answers to one of our most profound questions: Are we alone in the cosmos, or is life thriving in the vast ocean worlds of distant stars?
A Statistical Argument
The absence of evidence does not rule out the possibility of extraterrestrial life. Astrobiology focuses on searching for signs of life beyond Earth. In the absence of direct proof, the strongest case for alien life comes from statistics. Given the vast number of planets in the universe, it is likely that life has emerged elsewhere, too.
This idea is captured by the Drake Equation, which estimates the number of intelligent civilisations in our galaxy based on factors like star formation rates, the number of habitable planets, and the likelihood of life developing and becoming intelligent. Due to uncertainties in these values, the equation’s results vary widely—from suggesting Earth is unique to predicting millions of civilisations. While not a scientific fact, the Drake Equation is a useful tool for estimating the probability of intelligent extraterrestrial life.
© Spectrum Books Pvt Ltd.
