Giant exoplanet composition: Why do the hydrogen-helium equation of state and interior structure matter?
Saburo Howard, Ravit Helled, Simon M"uller
arXiv:2410.21382v1 Announce Type: new
Abstract: Revealing the internal composition and structure of giant planets is fundamental for understanding planetary formation. However, the bulk composition can only be inferred through interior models. As a result, advancements in modelling aspects are essential to better characterise the interiors of giant planets. We investigate the effects of model assumptions such as the interior structure and the hydrogen-helium (H-He) equation of state (EOS) on the inferred interiors of giant exoplanets. We first assess these effects on a few test cases and compare H-He EOSs. We then calculate evolution models and infer the planetary bulk metallicity of 45 warm exoplanets, ranging from 0.1 to 10~$M_{rm J}$. Planets with masses between about 0.2 and 0.6~$M_{rm J}$ are most sensitive to the H-He EOS. Updating the H-He EOS reduces the inferred heavy-element mass, with an absolute difference in bulk metallicity of up to 13%. Concentrating heavy elements in a core, rather than distributing them uniformly (and scaling opacities with metallicity), reduces the inferred metallicity (up to 17%). The assumed internal structure, along with its effect on the envelope opacity, has the greatest effect on the inferred composition of massive planets ($M_{rm p}>4~M_{rm J}$). For $M_{rm p}>0.6~M_{rm J}$, the observational uncertainties on radii and ages lead to uncertainties in the inferred metallicity (up to 31%) which are larger than the ones associated with the used H-He EOS and the assumed interior structure. However, for planets with $0.2
Abstract: Revealing the internal composition and structure of giant planets is fundamental for understanding planetary formation. However, the bulk composition can only be inferred through interior models. As a result, advancements in modelling aspects are essential to better characterise the interiors of giant planets. We investigate the effects of model assumptions such as the interior structure and the hydrogen-helium (H-He) equation of state (EOS) on the inferred interiors of giant exoplanets. We first assess these effects on a few test cases and compare H-He EOSs. We then calculate evolution models and infer the planetary bulk metallicity of 45 warm exoplanets, ranging from 0.1 to 10~$M_{rm J}$. Planets with masses between about 0.2 and 0.6~$M_{rm J}$ are most sensitive to the H-He EOS. Updating the H-He EOS reduces the inferred heavy-element mass, with an absolute difference in bulk metallicity of up to 13%. Concentrating heavy elements in a core, rather than distributing them uniformly (and scaling opacities with metallicity), reduces the inferred metallicity (up to 17%). The assumed internal structure, along with its effect on the envelope opacity, has the greatest effect on the inferred composition of massive planets ($M_{rm p}>4~M_{rm J}$). For $M_{rm p}>0.6~M_{rm J}$, the observational uncertainties on radii and ages lead to uncertainties in the inferred metallicity (up to 31%) which are larger than the ones associated with the used H-He EOS and the assumed interior structure. However, for planets with $0.2
2024-10-30
