Species abundances in WASP-77A

It has recently been reported that the hot Jupiter WASP-77Ab has subsolar atmospheric carbon and oxygen abundances with a solar C/O abundance ratio. Assuming solar carbon and oxygen abundances for its host star WASP-77A, WASP-77Ab's atmospheric carbon and oxygen abundances possibly indicate that it accreted its envelope interior to its parent protoplanetary disk's H2O ice line from carbon-depleted gas with little subsequent planetesimal accretion or core erosion.

We show that the photospheric abundances of carbon and oxygen in WASP-77A are supersolar with a subsolar C/O abundance ratio, implying that WASP-77Ab's atmosphere has significantly substellar carbon and oxygen abundances with a superstellar C/O ratio. Our result possibly indicates that WASP-77Ab's envelope was accreted by the planet beyond its parent protoplanetary disk's H_2_O ice line. While numerous theoretical complications to these idealized models have now been identified, the possibility of nonsolar protoplanetary disk abundance ratios confound even the most sophisticated protoplanetary disk and giant planet formation models.