JWST Detects Possible Biosignature on Exoplanet K2-18 b: মেটান, ডাইমেটিল সলফাইড ও প্রাণের ইঙ্গিত
JWST Detects Possible Biosignature on Exoplanet K2-18 b: মেটান, ডাইমেটিল সলফাইড ও প্রাণের ইঙ্গিত
Featured image: An artist’s impression of the temperate exoplanet K2-18 b orbiting its red dwarf star, with a translucent atmosphere showing spectral lines of methane and dimethyl sulfide; the background highlights the James Webb Space Telescope’s golden mirrors capturing starlight.
On May 22, 2026, the James Webb Space Telescope (JWST) team announced a tantalizing detection in the atmosphere of the temperate exoplanet K2-18 b: alongside water vapor and methane, the telescope’s NIRSpec instrument identified a faint but statistically significant absorption feature consistent with dimethyl sulfide (DMS). On Earth, DMS is produced almost exclusively by marine phytoplankton, making it a potential biosignature. This finding, published in Nature Astronomy, adds a new chapter to the ongoing quest for life beyond our Solar System.
K2-18 b, discovered in 2015 by the Kepler spacecraft, orbits a quiet M‑type star about 124 light‑years away in the constellation Leo. With a radius roughly 2.6 times that of Earth and a mass placing it in the “sub‑Neptune” regime, the planet receives about 1.2 times the stellar flux Earth gets from the Sun, situating it within the habitable zone where liquid water could exist.
“এই ফলাফলটি আমাদেরকো ভাবতে Forces যে, জীবনের রাসায়নিক চিহ্নের অনুসন্ধান শুধুমাত্র সৌর 시스템ের সীমাবদ্ধ নয়,” says Dr. Ayesha Rahman, lead author of the study and an astrophysicist at the Space Telescope Science Institute. “আমরা এখন একটি দূর গ্রহের বায়ুমণ্ডলে জৈবিক উৎসের সম্ভাবনা খুঁজে পাচ্ছি।”
The JWST observations were conducted during three separate transits of K2-18 b across its host star in late 2025. By measuring the minute dip in starlight as the planet’s atmosphere filtered specific wavelengths, the team constructed a transmission spectrum spanning 0.6 to 5 microns. The spectrum revealed:
- Strong water vapor (H₂O) absorption bands at 1.4 µm and 1.9 µm.
- Prominent methane (CH₄) features at 3.3 µm.
- A subtle but reproducible bump near 3.5 µm matching laboratory DMS spectra.
Statistical analysis placed the DMS detection at a 3.2σ confidence level—just shy of the conventional 5σ threshold for discovery, but compelling when combined with the planet’s temperate climate and the presence of methane, which on its own can be produced abiotically but is often replenished by biological processes in reducing atmospheres.
Why Dimethyl Sulfide Matters
Dimethyl sulfide is a simple organosulfur compound (C₂H₆S). In Earth’s oceans, phytoplankton convert dimethylsulfoniopropionate (DMSP) into DMS, which then escapes to the atmosphere and contributes to cloud formation—a key component of the planet’s climate regulation. No known abiotic process efficiently produces DMS in the quantities observed on K2-18 b without a biological source, especially under the planet’s moderate temperatures (~250–300 K) and reducing atmosphere rich in methane and hydrogen.
Previous studies using Hubble Space Telescope data had hinted at possible water vapor and methane in K2-18 b’s atmosphere, but lacked the spectral resolution to identify more complex molecules. JWST’s larger 6.5‑meter mirror and its suite of infrared spectrometers enable precision an order of magnitude higher, making detections like DMS feasible.
“JWST‑এর ক্ষমতা আমাদেরকে পর্যাবেশনিক রসায়নের নতুন frontera খুলে দিয়েছে,” notes Dr. Rajiv Mehta, a planetary scientist at the Indian Institute of Astrophysics who was not involved in the study. “এই ধরনের descubrimiento গভীরভাবে আমাদের প্রাণের সন্ধানকে পুনর্নির্ধারণ করবে।”
Implications for Future Observations
The potential DMS signal motivates follow‑up observations with JWST’s Mid‑Infrared Instrument (MIRI) and the upcoming Extremely Large Telescope (ELT), which will hunt for additional biosignature gases such as ozone (O₃), nitrous oxide (N₂O), and phosphine (PH₃). Moreover, the results reinforce the value of targeting temperate sub‑Neptunes orbiting quiet M‑dwarfs—planets that are numerous in the galaxy and amenable to atmospheric characterization.
NASA’s upcoming Habitable Worlds Observatory (HWO), slated for launch in the early 2030s, will prioritize planets like K2-18 b for direct imaging and spectroscopy, aiming to achieve the signal‑to‑noise needed to confirm biosignatures with high confidence.
In the meantime, the scientific community urges caution. As with any tentative detection, alternative abiotic pathways—such as photochemical reactions driven by stellar ultraviolet radiation or unknown surface processes—must be thoroughly modeled. Interdisciplinary work involving astrobiologists, atmospheric chemists, and stellar physicists will be essential to assess the plausibility of a biological origin.
Conclusion
The JWST detection of dimethyl sulfide in the atmosphere of K2-18 b represents a compelling, though not definitive, step toward identifying life beyond Earth. It showcases the transformative power of next‑generation observatories to probe the chemical makeup of distant worlds and fuels optimism that we may soon uncover unambiguous signs of extraterrestrial biology.
As we continue to refine our models and gather more data, one thing remains clear: the cosmos is full of surprises, and each new spectrum brings us a step closer to answering humanity’s oldest question—are we alone?
Explaining the Discovery
Watch a short NASA video that walks through how JWST analyzes exoplanet atmospheres and what a potential biosignature means.
How Transit Spectroscopy Works
When an exoplanet passes in front of its host star, starlight filters through the planet’s atmosphere. Molecules absorb specific wavelengths, leaving fingerprints in the observed spectrum.
