Attempting to determine the precise compositions of exoplanets has a number of significant challenges. Even some of the more recent works utilizing the James Webb Space Telescope are not quite at the necessary noise resolution limits to obtain the precise spectra of nearby sub-Neptunes and terrestrial exoplanets.
One of the more recent methodologies to extract the spectral signal from the noise has been to use Bayesian modeling techniques. This statistical method utilizes the inferences of difference chemical species to attempt to rule out competing molecular spectral overlaps and end up with a highly probable answer of what produced the spectral absorption line. The problem is that Bayesian inference requires prior distributions to produce posterior probabilities. Key point: we don't have prior exoplanet data to utilize.
In a recent paper by Welbanks, et al. (2026) they note that some of the earlier claims of molecular detection on exoplanet K2-18b may be erroneous since they were able to show "numerous alternatives providing equally good or better fits." In the graph below they show that multiple hydrocarbons can produce significant overlaps.
This critique won't last long, however. Improvements in instrumentation along with the Nancy Grace and Pandora space telescopes will start clarifying the data. Clearly a Level 1 approach.
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