Observable Differences Between Core Accretion and Disk Instability

摘要

There are two competing paradigms for giant planet formation: core accretion and disk instability. In core accretion, solid particles in a pro-toplanetary disk coagulate into larger and larger bodies until a core massive enough to accrete a gaseous envelope forms, on time scales of millions of years. In disk instability, the disk fragments into a self-gravitating giant planet-sized clump, within tens of thousands of years. How and when giant planets form affect whether or not other planets in that system are habitable. To address this problem, I present predictions of what planet-forming disks might look like by modeling patterns of shadowing and illumination from the central star on the disks surfaces. I model the signature of core accretion in an analytic disk model of a quiescent disk that is perturbed by a 10-20 Earth mass body. The perturbation in the disk image follows the position of the planet. I model the signature of disk instability in a 3D hydrodynamic simulation of a disk in which a planet-sized clump is forming (Boss 2001). In this case, the disk is optically thick and stirred up by the forming planet, so the exact location of the protoplanet is indeterminate. However, the high variability and corrugated structure in the disk images are in and of themselves indicators that gravitational instability is occuring. In either case, milliarcsecond resolution is necessary to image the per-turbations. This might be achievable by the GMT or TMT in optical/near-IR, or by ALMA in radio.