When Protoplanetary Disks are Gravitationally Unstable, Planetesimals can Collide, Grow Larger Than 1 Meter

ORBITAL SURVIVAL OF METER-SIZE AND LARGER BODIES DURING GRAVITATIONALLY UNSTABLE PHASES OF PROTOPLANETARY DISK EVOLUTION

Author:

Boss

Abstract:

A long-standing problem in the collisional accretion of terrestrial planets is the possible loss of m-size bodies through their inward migration onto the protostar as a result of gas drag forces. Such inward migration can be halted, and indeed even reversed, in a protoplanetary disk with local pressure maxima, such as marginally gravitationally unstable (MGU) phases of evolution, e.g., FU Orionis events. Results are presented for a suite of three-dimensional models of MGU disks extending from 1 to 10 AU and containing solid particles with sizes of 1 cm, 10 cm, 1 m, or 10 m, subject to disk gas drag and gravitational forces. These hydrodynamical models show that over disk evolution time scales of $\sim 6\times {10}^{3}$ years or longer, during which over half the gaseous disk mass is accreted by the protostar, very few 1 and 10 m bodies are lost through inward migration: most bodies survive and orbit stably in the outer disk. A greater fraction of 1 and 10 cm particles are lost to the central protostar during these time periods, as such particles are more closely tied to the disk gas accreting onto the protostar, but even in these cases, a significant fraction survive and undergo transport from the hot inner disk to the cold outer disk, perhaps explaining the presence of small refractory particles in Comet Wild 2. Evidently MGU disk phases offer a means to overcome the m-sized migration barrier to collisional accumulation.