Discovered in 2015 by NASA’s Kepler space telescope, K2-18b is a distant world orbiting a red dwarf star 124 light-years away. This exoplanet is 2.6 times wider and 8.6 times more massive than Earth, with a 33-day orbit (that is just over one month for us!) snugly within its star’s habitable zone—the region where temperatures could allow liquid water! Early Hubble observations in 2019 revealed water vapor in its atmosphere, sparking debates about its potential to host life. But it wasn’t until 2023–2025 that NASA’s James Webb Space Telescope (JWST) delivered groundbreaking data, transforming K2-18b into the most promising candidate for extraterrestrial biology.
Using JWST’s unmatched sensitivity, a team led by Professor Nikku Madhusudhan (University of Cambridge) detected methane (CH₄), carbon dioxide (CO₂), and—most intriguingly—dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the planet’s atmosphere. How did they do this? Well, the JWT uses something called ultra-sensative infrared sensors! This means the the telescope can capture starlight that has gone through the planet’s atmosphere, in which they can then find ‘chemical’ fingerprints in the spectrum and identify the molecules in the atmosphere.
On Earth, these sulfur-rich gases (DMS and DMDS) are exclusively produced by living organisms, such as marine plankton. Even more astonishing, their concentrations on K2-18b are thousands of times higher than Earth’s levels, suggesting that the planet could , as prof Madhusudhan said, be ‘teeming wtih life’
This aligns with the Hycean world hypothesis—a theoretical class of planets with hydrogen-rich atmospheres overlying vast liquid water oceans. Fun fact: K2-18B is in the ‘Hycean goldilocks zone’ in it’s system.
Promblems that are faced
While the findings are electrifying, the team stresses that this is not yet proof of life. The detection of DMS/DMDS sits at a 3-sigma1 confidence level—a 99.7% likelihood the signal is real, but still short of the 5-sigma gold standard (99.99994% or a one in a million chance to fluke) required for definitive claims. Skeptics like Ryan MacDonald (University of Michigan) note that previous “exciting” signals from K2-18b later faded under scrutiny. On top of this, volcanic activity or exotic chemistry in a hydrogen-rich environment might also generate DMS, which could mean that life forms aren’t definite.
- Sigma … is a unit of measurment referring to the amount of variability in a set of data. In our case we want little to no variability, which is a 5 Sigma confidence level, and some time ago, a test we did on a planet came to 1 Sigma, or about 65-70% confidence level.
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What’s Next?
Madhusudhan’s team plans 16–24 additional hours of JWST observations to boost confidence to 5-sigma. If confirmed, K2-18b would become humanity’s first credible candidate for hosting life beyond Earth—a revelation that could redefine our place in the cosmos.
But after all this, the excitement about a new planet with life is great and all, and that we might not be alone in the Solar System, but people are already assuming its a place to go to after Earth fails. The question is, what is the point in finding new planets to possibly destroy alongside our own?