Dix Planetary Science Seminar

Speaker: Aida Behmard

Title: How Common is Planet Engulfment?

Abstract: Dynamical evolution in planetary systems can cause planets to be engulfed by their host stars, which can be detected through refractory abundance enhancements due to rocky material accretion. Multi-star systems are excellent environments to search for signs of engulfment because these stars share the same natal gas cloud and primordial chemical compositions. Thus, refractory differences between stellar companions constitute a signpost of planet engulfment. Several multi-star systems are reported to exhibit engulfment signatures. However, only a handful of systems have been searched for such signatures so far. We propose targeting 40 planet host systems to obtain refractory element measurements at precisions of <~ 0.03 dex. This sample will allow us to assess the prevalence of planet engulfment and its role in the evolution of systems with existing planets, and examine chemical homogeneity in planet-hosting multi-star systems.

Speaker: Elizabeth Bailey

Title: Thermodynamically Governed Interior Models of Uranus and Neptune

Abstract: It is often suggested that Uranus and Neptune may be the solar system's representatives of the mid-size planets now known to be widespread among planetary systems. But despite the apparent importance of the so-called "ice giants" in contextualizing our planetary system's formation, the bulk compositions of Uranus and Neptune are poorly constrained relative to the other solar system planets. Specifically, a wide range of interior distributions of light, medium, and heavy constituents can satisfy the observed masses, radii, and gravitational harmonics of Uranus and Neptune. This compositional degeneracy is a longstanding challenge inherent to mid-size planets. In this talk, I will discuss results from a novel approach to modeling the interiors of Uranus and Neptune by accounting for inferred mixing properties of hydrogen and water at conditions of the deep interiors. I will demonstrate that the observed gravity harmonics and magnetic fields of Uranus and Neptune are consistent with hydrogen-water demixing in the deep interiors. Furthermore, in this model framework, Neptune--but not Uranus--is currently expected to have a substantial fraction of water (≳10 mol%) in its outer, hydrogen-rich shell, suggesting incomplete hydrogen-water demixing in Neptune. I will discuss how this finding may offer a potential explanation for the paradox of these planets' differing intrinsic heat fluxes.