Located 124 light-years from Earth, a planet classified as a super-Earth or mini-Neptune is exciting astronomers. The latest observations from the James Webb Telescope reveal characteristic molecules in its atmosphere, reigniting the debate about extraterrestrial life.
This discovery is based on meticulous analysis of light filtered through the atmosphere of K2-18b. Although the results do not constitute definitive proof, they open a new era in the search for biosignatures beyond the Solar System.
Chemical clues of potential life
Researchers have found what they identified as dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), compounds associated with biological activity on Earth. These molecules, detected with 99.7% statistical certainty, could suggest the presence of microorganisms in an ocean environment.
However, these substances could also originate from unknown geochemical processes. The observed concentrations are thousands of times higher than on our planet, a phenomenon that puzzles scientists.
The University of Cambridge team remains cautious, emphasizing the need for further verification. The James Webb Telescope will require between 16 and 24 additional hours of observation to confirm these results.
A hybrid world with multiple hypotheses
K2-18b, eight times more massive than Earth, orbits a red dwarf in 33 days. Some models suggest it could host a vast ocean beneath a hydrogen-rich atmosphere, while others propose it might be a gaseous or volcanic planet.
Critics point to high temperatures and the lack of direct evidence of liquid water. The previous detection of methane, initially interpreted as water vapor, illustrates the persistent uncertainties.
Despite these disagreements, K2-18b remains a unique laboratory for studying habitability conditions. Future observations could determine whether it's a hostile world or a potential ecosystem.
Going further: How does the James Webb Telescope analyze atmospheres?
The JWST uses a technique called transmission spectroscopy. When an exoplanet passes in front of its star, a tiny fraction of the light passes through its atmosphere. Present molecules absorb specific wavelengths, creating distinctive patterns in the light spectrum.
The telescope's MIRI instrument, specialized in mid-infrared, is particularly suited for detecting complex organic molecules. Unlike previous telescopes, its sensitivity allows identification of compounds even in low concentrations. This technology was essential for spotting dimethyl sulfide on K2-18b.
The analysis relies on comparison with theoretical models and experimental data. Scientists must eliminate potential interferences and confirm that spectral signatures truly match the suspected molecules. This rigorous process explains why multiple observations are needed to validate a discovery.
Article author: Cédric DEPOND