Astronomers utilizing the NASA/ESA/CSA James Webb House Telescope have detected the chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) within the ambiance of the super-Earth exoplanet K2-18b. On Earth, DMS and DMDS are solely produced by life, primarily microbial life reminiscent of marine phytoplankton. Whereas an unknown chemical course of would be the supply of those molecules in K2-18b’s ambiance, the outcomes are the strongest proof but that life might exist on an extrasolar planet.
An artist’s impression of the super-Earth exoplanet K2-18b. Picture credit score: A. Smith / N. Mandhusudhan.
K2-18 is a purple dwarf positioned roughly 111 light-years away within the constellation of Leo.
Also called EPIC 201912552, the star hosts two huge exoplanets: K2-18b and K2-18c.
First found in 2015, K2-18b has a radius of two.6 occasions that of Earth and is about 8.6 occasions as huge.
The planet orbits its star each 33 days at a distance of roughly 0.15 AU and has an Earth Similarity Index of 0.73.
It receives 1.28 occasions the sunshine depth of Earth, and its equilibrium temperature is minus 2 levels Celsius (28 levels Fahrenheit).
Earlier observations of K2-18b recognized methane and carbon dioxide in its ambiance. This was the primary time that carbon-based molecules had been found within the ambiance of an exoplanet within the liveable zone.
These outcomes had been according to predictions for a Hycean world: a liveable ocean-covered exoplanet beneath a hydrogen-rich ambiance.
Nevertheless, one other, weaker sign hinted at the potential for one thing else taking place on K2-18b.
Transmission spectrum of K2-18b utilizing Webb’s MIRI spectrograph. Picture credit score: A. Smith / N. Mandhusudhan.
“We didn’t know for positive whether or not the sign we noticed final time was resulting from DMS, however simply the trace of it was thrilling sufficient for us to have one other look with Webb utilizing a distinct instrument,” stated Professor Nikku Madhusudhan, an astronomer with the Institute of Astronomy on the College of Cambridge.
The sooner, tentative, inference of DMS was made utilizing Webb’s NIRISS (Close to-Infrared Imager and Slitless Spectrograph) and NIRSpec (Close to-Infrared Spectrograph) devices, which collectively cowl the near-infrared (0.8-5 micron) vary of wavelengths.
The brand new, impartial statement used Webb’s MIRI (Mid-Infrared Instrument) within the mid-infrared (6-12 micron) vary.
“That is an impartial line of proof, utilizing a distinct instrument than we did earlier than and a distinct wavelength vary of sunshine, the place there is no such thing as a overlap with the earlier observations. The sign got here via robust and clear,” Professor Madhusudhan stated.
“It was an unimaginable realization seeing the outcomes emerge and stay constant all through the intensive impartial analyses and robustness exams,” added Dr. Måns Holmberg, an astronomer on the House Telescope Science Institute.
DMS and DMDS are molecules from the identical chemical household, and each are predicted to be biosignatures.
Each molecules have overlapping spectral options within the noticed wavelength vary, though additional observations will assist differentiate between the 2 molecules.
Nevertheless, the concentrations of DMS and DMDS in K2-18b’s ambiance are very completely different than on Earth, the place they’re typically under one half per billion by quantity.
On K2-18b, they’re estimated to be 1000’s of occasions stronger — over ten elements per million.
“Whereas the outcomes are thrilling, it’s very important to acquire extra knowledge earlier than claiming that life has been discovered on one other world,” Professor Madhusudhan stated.
“The inference of those biosignature molecules poses profound questions regarding the processes that could be producing them” stated Dr. Subhajit Sarkar, an astronomer at Cardiff College.
“Our work is the place to begin for all of the investigations that are actually wanted to verify and perceive the implications of those thrilling findings,” stated Dr. Savvas Constantinou, an astronomer with the Institute of Astronomy on the College of Cambridge.
“It’s vital that we’re deeply sceptical of our personal outcomes, as a result of it’s solely by testing and testing once more that we can attain the purpose the place we’re assured in them. That’s how science has to work,” Professor Madhusudhan stated.
The examine was printed immediately within the Astrophysical Journal Letters.
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Nikku Madhusudhan et al. 2025. New Constraints on DMS and DMDS within the Environment of K2-18b from JWST MIRI. ApJL 983, L40; doi: 10.3847/2041-8213/adc1c8