Extended Data Fig. 7: Carbon isotopic abundance analysis.

The top row of histograms compares the constraints from a nominal simplified retrieval model applied to the true data (red) and the reverse-injected data reinjected with ¹³C isotope removed model (black). The upper limit on the simulated data and bounded constraint arising from the true dataset suggests that there is indeed isotopic information in these IGRINS data. The bottom panel compares the retrieved ¹²C to ¹³C ratio (red) to common Solar System bodies (blue, after ref. ⁶⁷) and various reference values (galactic interstellar medium (ISM) components, and Earth (terrestrial), black dashed lines). WASP-77Ab sits anomalously low (enhanced ¹³C) compared to most Solar System objects.