Free Astronomy Magazine July-August 2025

9 JULY-AUGUST 2025 ASTRO PUBLISHING dance of carbon dioxide (CO 2 ), while the signals of ammonia (NH 3 ) and carbon monoxide (CO) were absent, a scenario in good agreement with the hycean model developed by Madhusudhan’s team. It is in these same spectra that the researchers believed they recognized for the first time the possible traces of DMS, or alternatively DMDS (dimethyl disulfide, CH 3 S 2 CH 3 ), another biosig- nature, superimposable to the first in terms of spectral properties. How- ever, it was a feeble signal with little statistical relevance that could have been generated by random fluctua- tions, noise, or measurement errors. The 2024 observations After using Webb for just over ten hours in 2023, Madhusudhan’s team was given an additional period of nearly six hours to obtain more transmission spectra of K2-18 b tran- siting in front of the disk of its star. The new observations took place be- tween April 25 and 26, 2024, using on that occasion the MIRI spectro- graph (Mid-Infrared Instrument, op- erating in the 5-28 microns range). Looking for biosignatures with a dif- ferent instrument from the previous ones, in an infrared band adjacent and complementary to that covered by the other two spectrographs, would have given credibility to the DMS (or DMDS) signal if it had man- ifested itself again. And “the signal came through loud and clear,” com- mented Madhusudhan, who added: “This is an independent line of evi- dence, using a different instrument in a different wavelength range, where there is no overlap with pre- vious observations.” The new investigation would seem to have strengthened the hypothe- sis of the presence of life on K2-18 b, provided that all the assumptions that led researchers to interpret S hown here are transmission spectrum data acquired by the Mid-Infrared In- strument (MIRI) on board JWST, as it examined the atmosphere of the tran- siting exoplanet K2-18 b. Error bars are shown in red at each data point, while the best-fit overall spectrum is shown by the blue line. These are the measure- ments that prompted Madhusudhan's team to announce the possible presence of life on K2-18 b. [N. Madhusudhan et al., 2024] A lthough the JWST MIRI spectrum of exoplanet K2-18 b is consistent with a series of light molecules like methane and carbon dioxide along with DMS and/or DMDS, the “significance” of 3-sigma was only obtained because all other possible gas species that could exhibit a strong absorption feature beginning at 9 microns were excluded from the analysis. There are other strongly viable scenarios that must be considered as well. In scientific contexts, sigma ( σ ) quan- tifies the variability or dispersion of data points around the mean. A higher sigma level indicates greater confidence in a result, meaning it is less likely to be due to chance or noise. 3-sigma is a very favorable value but does not certify a discovery. [N. Madhusudhan et al., 2024] those traces, in truth ethereal, as biosignatures are considered valid. Among those assumptions, there are quite a few scenarios proposed in the form of scientific articles by Madhusudhan himself, which makes the conclusions he and his team reach somewhat self-referential.