In a breakthrough that has electrified the astrobiology community, scientists observing the exoplanet K2‑18b with the James Webb Space Telescope (JWST) have detected signs of alien life: gases that on Earth are strongly linked to biological activity. As detailed in a peer-reviewed study published in The Astrophysical Journal Letters, this discovery may represent the most compelling evidence yet that life could exist beyond our solar system.
The exoplanet, located 124 light-years away, has previously drawn attention for its potential habitability. But now, the detection of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS)—gases that are exclusively produced by life on Earth—has pushed K2-18b to the forefront of the search for extraterrestrial life.
Spectral Signatures That Set K2-18b Apart
Using Webb’s powerful Mid-Infrared Instrument (MIRI), astronomers captured light from K2‑18b as it passed in front of its host star. This method, known as transit spectroscopy, allows scientists to analyze the chemical composition of an exoplanet’s atmosphere. In this case, they found a surprisingly strong signature of sulfur-bearing compounds, particularly dimethyl sulfide.
What makes this finding remarkable is that DMS is not known to occur through any abiotic process on Earth. On our planet, it is released primarily by marine phytoplankton—tiny ocean-dwelling organisms. On K2‑18b, the detected concentrations were over 10 parts per million, thousands of times greater than what is found in Earth’s atmosphere. Scientists believe that such levels could only be maintained if a biological source is continuously replenishing the gas.
The discovery doesn’t yet qualify as definitive proof of life, as it meets the three-sigma threshold—meaning there’s only a 0.3% chance the signal is due to random noise. Confirmation in science requires a five-sigma threshold, equivalent to a 0.00006% probability of error. Still, reaching three-sigma at such distance is already historic.
What Makes K2‑18b So Intriguing
K2‑18b, discovered in 2015, is a Hycean world—a type of exoplanet that is larger than Earth but smaller than Neptune, with a hydrogen-rich atmosphere and potentially liquid oceans beneath. With a mass about 8.6 times that of Earth and a diameter 2.6 times greater, it sits firmly in the habitable zone of a cool red dwarf star. This means the planet receives just enough light and heat to keep surface water in a liquid state, a key requirement for life as we know it.
The latest observations support earlier hints of sulfur-based chemistry seen through different instruments, but this new dataset—captured with longer infrared wavelengths—strengthens the case that biological processes may be involved. The consistency of the signal across independent instruments and analysis methods adds to the growing confidence among researchers.
The Debate: Biosignature or False Alarm?
Despite the excitement, scientists remain cautious. Alternative explanations include non-biological photochemical processes or geological emissions that could, in theory, produce DMS and DMDS. However, the combination of observed gases, planetary conditions, and atmospheric dynamics strongly favors a biological origin.
“Earlier theoretical work had predicted that high levels of sulfur-based gases like DMS and DMDS are possible on Hycean worlds,” said Professor Nikku Madhusudhan, lead author of the study. “And now we’ve observed it, exactly as predicted. Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have.”
Co-author Subhajit Sarkar added, “The inference of these biosignature molecules poses profound questions concerning the processes that might be producing them.” The team agrees that additional telescope time, between 16 and 24 hours, would be sufficient to reach the five-sigma milestone and confirm the presence of life-related chemistry.
What’s Next in the Hunt for Life?
While JWST has made this discovery possible, future observatories like the Habitable Worlds Telescope and the European Extremely Large Telescope will offer even sharper instruments to examine smaller, Earth-sized worlds with greater spectral resolution. If future observations confirm DMS or other biosignatures across multiple planets, it could mark a new chapter in humanity’s understanding of life in the universe.
“This could be the tipping point,” said Madhusudhan. “Where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.”
Source: The Daily Galaxy / Digpu NewsTex