Could Planet Nine Have Formed in its Current Orbit

Making Planet Nine: Pebble Accretion at 250--750 AU in a Gravitationally Unstable Ring

Authors:

Kenyon et al

Abstract:

We investigate the formation of icy super-Earth mass planets within a gravitationally unstable ring of solids orbiting at 250-750 AU around a 1 solar mass star. Coagulation calculations demonstrate that a system of a few large oligarchs and a swarm of pebbles generates a super-Earth within 100-200 Myr at 250 AU and within 1-2 Gyr at 750 AU. Systems with more than ten oligarchs fail to yield super-Earths over the age of the solar system. As these systems evolve, destructive collisions produce detectable debris disks with luminosities of 10−5 to 10−3 relative to the central star.