Satellitesimal Formation via Collisional Dust Growth in Steady Circumplanetary Disks

Abstract

The icy satellites around Jupiter are considered to have formed in a circumplanetary disk. While previous models focused on the formation of satellites starting from satellitesimals, the question of how satellitesimals form from smaller dust particles has not been addressed so far. In this work, we study the possibility that satellitesimals form in situ in a circumplanetary disk. We calculate the radial distribution of the surface density and representative size of icy dust particles that grow by colliding with each other and drift toward the central planet in a steady circumplanetary disk with a continuous supply of gas and dust from the parent protoplanetary disk. The radial drift barrier is overcome if the ratio of the dust to gas accretion rates onto the circumplanetary disk,Ṁ d /Ṁ g , is high and the strength of turbulence, α, is not too low. The collision velocity is lower than the critical velocity of fragmentation when α is low. Taken together, we find that the conditions for satellitesimal formation via dust coagulation are given byṀ d /Ṁ g ≥ 1 and 10 −4 ≤ α < 10 −2 . The former condition is generally difficult to achieve, suggesting that the in-situ satellitesimal formation via particle sticking is viable only under an extreme condition. We also show that neither satellitesimal formation via the collisional growth of porous aggregates nor via streaming instability is viable as long asṀ d /Ṁ g is low.

Including Dust Coagulation in Hydrodynamic Models of Protoplanetary Disks: Dust Evolution in the Vicinity of a Jupiter-mass Planet

“…Lambrechts et al 2014;Ataiee et al 2018;Bitsch et al 2018). However, our results suggest that those large grains will fragment and constantly replenish the population of small grains, which are able to pass through the gap and potentially re-grow in the planet co-orbital region (although the resolution of our models does not allow us to resolve the potential circumplanetary disk, in which the growth would be most efficient, see Shibaike et al 2017;Drażkowska & Szulágyi 2018). Dust coagulation and fragmentation could thus increase the pebble isolation mass.…”

The Galilean Satellites Formed Slowly from Pebbles

“…We calculate the evolution of dust particles in the CJD using a 1-D single-size analytical formula (Shibaike et al 2017). They grow to pebbles and then drift to Jupiter because the gas disk rotates with sub-Kepler velocity which is slower than the rotating velocity of the pebbles so that they lose their angular momentum.…”

“…In the geometric limit (pebbles larger than the wavelength), the opacity of pebbles is given by κ p ∼ 1/(ρ int,p a p ), where ρ int,p and a p are the pebble internal density and the pebble radius, respectively. If the pebbles are fluffy, the opacity of pebbles could be κ p ∼ 1/(10 −3 × 10) = 10 2 cm 2 g −1 (Kataoka et al 2014;Shibaike et al 2017). In this case, the mean optical depth of pebbles is τ p = κ p Σ p ∼ 10 2 × 10 −2 = 1 (see Figure 3).…”

“…However the main problem with this scenario is that in-situ satellitesimal formation requires dust-to-gas ratios ∼ 1 (Carrera et al 2015;Yang et al 2017), which is not reached by far because of the very fast pebble drift in the CJD (Shibaike et al 2017). The increase in ice surface density by a factor 3-5 at the snowline , would not be enough by far.…”

Formation of single-moon systems around gas giants

“…We aim to find a way to form a system with only one large moon in a CPD. The feasibility of satellitesimal formation has been examined by Shibaike et al (2017) and delivery of solid matereal to a CPD has been discussed by Fujita et al (2012); Tanigawa et al (2014); Suetsugu & Ohtsuki (2017); Ronnet et al (2018). We focus on the later stage of the satellite formation and investigate the orbital evolution of the moons in a dissipating CPD to determine the final appearance of the system.…”