Extended Data Fig. 7: Retrieved volume mixing ratios from the POSEIDON retrievals of LHS 475 b’s transmission spectrum.
From: A JWST transmission spectrum of the nearby Earth-sized exoplanet LHS 475 b
Two retrievals with different prior treatments for the atmospheric composition are overplotted: centered log-ratio (CLR) transformed abundances with a priori unknown composition (green); and log-uniform abundances assuming an N2-dominated atmosphere (orange). Statistical 2σ upper and lower limits are annotated (or ‘N/A’ if unconstrained). Both retrievals rule out H2-dominated atmospheres. The log- uniform retrieval finds upper limits on H2O, CH4, CO2, and CO due to the assumption that N2 dominates the atmosphere, while the agnostic CLR treatment does not find upper limits for their abundances. For clarity in viewing upper limits, we switch from a logarithmic to linear x-axis at a mixing ratio of 10%. The probability densities for the linear histogram bins are renormalized to match the probability density of the nearest logarithmic bin left of the 10% boundary.
