Rocky planets reloaded:

Planet Formation and Trapping in Inner Magnetised Accretion Disks.

Mario Flock, Eric Gaidos, Myriam Benisty and Neal Turner

The discovery of more than 5000 planets around other stars (exoplanets) compels investigations of how their formed.

One paradigm-shifting finding from the last decade of exoplanet surveys has been the presence of Earth-size or “super-Earth”-size planets on close-in orbits with periods of a day to few tens of days – for which there is no analog in our Solar System.

The existence of these objects are both a challenge to traditional models of planet formation, and an opportunity – using new ground- and space-based observatories – to study the planet formation process and outcome with methods that cannot be applied to planets on wider orbits. Crucial to these investigations is better observations and modeling of the structure, dynamics, and composition of protoplanetary disks at comparable scales, and the inclusion of key processes: the role of magnetic fields from the star and advected or internally generated by the accretion disk; (magneto)-hydrodynamic instabilities in the disk; radiative transfer and feedbacks between temperature, opacity, and sublimation of silicates; solid-gas interactions from “pebbles” to entire planets.

We propose a KITP Program to bring together a broad range of expertise, including representatives of four cornerstone fields:

1) exoplanet observers, to provide the most current knowledge of the statistical distribution of close-in planets, their properties, and dependence on variables such as the stellar mass;

(2) disk modelers, to incorporate the latest methodological advances and self-
consistent integration of multiple physiochemical processes;

(3) disk observers, i.e. new instruments and techniques to probe the innermost regions (≪1 au) of disks; and

(4) geochemists and meteoritics, to supply expertise on processes involving the solid, liquid, and gas phases of rocky planet building blocks, and the early Solar System record which constrain these.

Each of these four areas is experiencing rapid advances, works within the context of a much larger, expanding field (e.g., exoplanet research in general), and usually has the opportunity to interact with a single other discipline. Our goal is catalyze integration of all four fields, but focused on a narrow range of parameter space. This approach will allow to address key questions: How are planets formed in these regions? How and where are the solid particles accumulated? What are the different planet assembly pathways? Are there any imprints of magnetic fields which where embedded in the disk? Are there any effects of the environment on the different planet assembly pathways of in-situ formation or inward migration?