No abstract

We present an overview of the formation of Jupiter and its associated circumplanetary disk. Jupiter forms via a combination of planetesimal accretion and gravitational accumulation of gas from the surrounding solar nebula. The formation of the circumjovian gaseous disk, or subnebula, straddles the transitional stage between runaway gas accretion and Jupiter's eventual isolation from the circumsolar disk. This isolation, which effectively signals the termination of Jupiter's accretion, takes place as Jupiter opens a deep gas gap in the solar nebula, or the solar nebula gas dissipates. The gap-opening stage is relevant to subnebula formation because the radial extent of the circumjovian disk is determined by the specific angular momentum of gas that enters Jupiter's gravitational sphere of influence. Prior to opening a well-formed, deep gap in the circumsolar disk, Jupiter accretes low specific angular momentum gas from its vicinity, resulting in the formation of a rotationally-supported compact disk whose size is comparable to the radial extent of the Galilean satellites. This process may allocate similar amounts of angular momentum to the planet and the disk, leading to the formation of an ab-initio massive disk compared to the mass of the satellites. As Jupiter approaches its final mass and the gas gap deepens, a more extended, less massive disk forms because the gas inflow, which must come from increasingly farther away from the planet's semimajor axis, has high specific angular momentum. Thus, the size of the circumplanetary gas disk upon inflow is dependent on whether or not a gap is present. We describe the conditions for accretion of the Galilean satellites, including the timescales for their formation and mechanisms for their survival, all within the context of key constraints for satellite formation models. The environment in which the regular satellites form is tied to the timescale for circumplanetary disk dispersal, which depends on the nature and persistence of turbulence. In the case that subnebula turbulence decays as gas inflow wanes, we present a novel mechanism for satellite survival involving gap opening by the largest satellites. On the other hand, assuming that sustained turbulence drives subnebula evolution on a short timescale compared to the satellite formation timescale, we review a model that emphasizes collisional processes to explain satellite observations. We briefly discuss the mechanisms by which solids may be delivered to the circumplanetary disk. At the tail end of Jupiter's accretion, most of the mass in solids resides in planetesimals of size > 1 km; however, planetesimals in Jupiter's feeding zone undergo a period of intense collisional grinding, placing a significant amount of mass in fragments < 1 km. Inelastic or gravitational collisions within Jupiter's gravitational sphere of influence allow for the mass contained in these planetesimal fragments to be delivered to the circumplanetary disk either through direct collisional/gravitational capture, or via ablation through the c...

constraints on the surface density of solids in the satellitesimal disk (excluding satellite embryos ∼ 1 g cm −2 for satellitesimals of size ∼ 1 km), which yields a total disk mass smaller than the mass of the regular satellites, and means that the satellites must form in several ∼ 10 collisional cycles. However, much more work will need to be conducted concerning the collisional evolution both of the circumplanetary satellitesimals and of the heliocentric planetesimals following giant planet formation before one can assess the significance of this agreement.Furthermore, for enough mass to be delivered to form the regular satellites in the required timescale one may need to rely on (unproven) mechanisms to replenish the feeding zone of the giant planet. We compare this model to the solids-enhanced minimum mass (SEMM) model of Mosqueira and Estrada (2003a,b), and discuss its main consequences for Cassini observations of the Saturnian satellite system.