A recent study builds upon intriguing findings from previous research regarding the potential existence of dimethyl sulfide, a chemical of interest for astrobiology. Utilizing the James Webb Space Telescope (JWST), the research team was able to capture images of K2-18b as it transits in front of its host star. During this event, some light filters through the planet’s atmosphere, providing a unique opportunity to analyze the chemical signatures present.
The team employed two distinct methods to analyze the spectral data obtained from JWST, and both techniques yielded consistent results. They investigated a combination of molecules that could generate a similar spectral signature, beginning with an initial list of 20 candidates. Ultimately, two chemicals emerged: dimethyl sulfide and dimethyl disulfide, although distinguishing between the two remains challenging with the current data.
On our planet, the natural production of dimethyl sulfide primarily occurs within living cells, leading researchers to propose that its presence on K2-18b might indicate biological activity. However, they also recognize that the statistical significance of the findings, currently measured at three sigma, does not firmly support a definitive discovery. Nevertheless, this observation is being characterized as the “strongest hints yet of biological activity,” according to a statement from the University of Cambridge.
Reasons for Doubt
Despite the compelling nature of these findings, skepticism persists among many astronomers. For a biosignature from an exoplanet to be convincing, it must pass several critical tests, encapsulated in three fundamental questions:
- Is the planet what we believe it to be?
- Is the signal authentic?
- Could other processes account for this signal?
Currently, none of these questions can be affirmed with certainty.
The first inquiry revolves around the classification of K2-18b as a hycean world. The researchers concede that the presence of an ocean on the planet is highly contingent on its atmospheric conditions: “A cloud-/haze-free atmosphere would render the surface too hot to be habitable and/or have water in a supercritical state.” Additionally, while data obtained from the JWST does not indicate the presence of clouds, the absence of evidence does not conclusively rule them out.
