Preferred mechanism of planet formation

Determine whether core accretion or gravitational instability is the preferred mechanism of planet formation in young planetary systems, focusing on establishing which scenario best explains observational evidence from directly imaged planets and protoplanets.

Background

The chapter contrasts the two leading theories for giant planet formation: core accretion and gravitational instability. It highlights how direct imaging uniquely probes young, wide-separation planets and protoplanets, providing spectra and system architecture that inform formation scenarios. Despite advances, the author notes that deciding which mechanism predominates across planetary systems remains unresolved.

Direct imaging captures photons from young and actively forming planets, and observations of systems like HR 8799, β Pictoris, and PDS 70 reveal diverse environments and dynamical histories. These data are central to testing formation models but have not yet yielded a definitive conclusion about the dominant mechanism.