Modeling Multiple Radius Valley Emergence Mechanisms With Multi-Transiting Systems

TL;DR

This study evaluates different mechanisms for the emergence of the radius valley in close-in exoplanets using multi-transiting systems, finding that multiple models can explain the observations but more data is needed for definitive conclusions.

Contribution

It extends the framework for testing radius valley formation mechanisms to multi-transiting systems, providing a comparative analysis of models against observed data.

Findings

Most systems can be explained by any of the three proposed mechanisms.

No significant trends with stellar mass or metallicity were found.

Additional mass measurements are needed for conclusive diagnostics.

Abstract

Close-in planets smaller than Neptune form two distinct populations composed of rocky super-Earths and sub-Neptunes that may host primordial H/He envelopes. The origin of the radius valley separating these two planet populations remains an open question and has been posited to emerge either directly from the planet formation process or via subsequent atmospheric escape. Multi-transiting systems that span the radius valley are known to be useful diagnostics of XUV-driven mass loss. Here, we extend this framework to test XUV-driven photoevaporation, core-powered mass loss, and an accretion-limited primordial radius valley model. Focusing on multi-transiting systems allows us to eliminate unobservable quantities that are shared within individual systems such as stellar XUV luminosity histories and the properties of the protoplanetary disk. We test each proposed radius valley emergence mechanism on all 221 known multi-transiting systems and calculate the minimum masses of the systems' enveloped planets to be consistent with the models. We compare our model predictions to 75 systems with measured masses and find that the majority of systems can be explained by any of the three proposed mechanisms. We also examine model consistency as a function of stellar mass and stellar metallicity but find no significant trends. More multi-transiting systems with mass characterizations are required before multi-transiting systems can serve as a viable diagnostic of radius valley emergence models. Our software for the model evaluations presented herein is available on GitHub and may be applied to future multi-transiting system discoveries.