New Study Questions Potential Biosignatures of Life on Exoplanet K2-18b

In the previous month, astronomers utilizing the James Webb Space Telescope generated significant attention by revealing indications of the substances dimethyl sulphide (DMS) and dimethyl disulfide (DMDS) on the exoplanet K2-18b, which is situated 124 light-years from Earth. These compounds are exclusively generated by living organisms, such as marine algae found on our planet, leading to their classification as potential «biosignatures» that could signify the presence of life. However, recent follow-up studies have raised questions regarding the validity of this detection. A new investigation spearheaded by researchers at the University of Chicago re-evaluated the data from the James Webb Space Telescope (JWST) and discovered that the evidence for DMS is considerably less convincing than initially suggested.

Diminishing Signals

In a recent arxiv preprint, which is pending peer review, Rafael Luque, Caroline Piaulet-Ghorayeb, and Michael Zhang employed a comprehensive methodology by synthesizing all JWST data across its main instruments (NIRISS, NIRSpec, and MIRI). Their findings indicate that the alleged DMS signal significantly weakens when all observations are integrated. Discrepancies in data processing and modeling between the original research also introduce uncertainty regarding the initial conclusions.

The researchers noted that even when signals resembling DMS arise, they are typically weak, inconsistent, and can frequently be attributed to alternative, non-biological compounds such as ethane. They emphasized the necessity for uniform modeling to prevent conflicting interpretations of planetary atmospheres.

Complexity of Spectra

Elements within an exoplanet’s atmosphere are generally identified through spectral analysis, which reveals distinctive «chemical fingerprints» by examining how the atmospheric composition absorbs certain wavelengths of starlight during its transit in front of its host star.

The distinction between DMS and ethane, a prevalent molecule in exoplanetary atmospheres, lies in a single sulfur atom. Although current spectrometers, including those aboard the JWST, exhibit remarkable sensitivity, they encounter limitations. The vast distances to exoplanets, the faintness of the signals, and the intricacies of atmospheres make it exceptionally difficult to differentiate between substances that vary by a mere atom. The recent assertion of a “3-sigma” detection of DMS does not meet the scientific threshold for verification. The team advocates for stricter standards in both scientific publishing and media coverage.