Formation of Water-rich Giant Planet Satellites at Decretion Disk Ice Lines

Abstract

The volatile budgets of giant planet satellites are critical to unraveling the origin of their building blocks within the circumplanetary disks that hosted them. The Galilean moons Ganymede and Callisto, as well as the Saturnian moon Titan, are known to be anomalously water rich on the basis of their mean densities and interior models informed by gravity data from Galileo and Cassini, characterized by ice-to-rock ratios around unity. Here, we show that the water-ice sublimation line in a decreting circumplanetary disk lends itself to the formation of a water-rich solid reservoir, serving as a natural site for the birthplace of icy satellites. Fundamentally, this reflects how interior to the ice line, water vapor is advected outward, while beyond it, water ice drifts inward as pebbles. Using a semi-analytic model for dust and vapor evolution, we simulate vapor and ice accumulation at the ice line, showing that solids just beyond it achieve steady-state ice-to-rock ratios a factor of a few higher than elsewhere in the disk. For typical disk parameters, this ice buildup occurs within a timescale of a few thousand years. We propose this as a first-order process that explains, at least to some extent, the compositions of three aforementioned satellites. We explore the impact of uncertain turbulence parameters on our results, namely the turbulent Schmidt number and Shakura-Sunyaev alpha, before discussing them in the context of icy satellite D/H ratios. We conclude by evaluating alternative scenarios for explaining water-rich satellites, based on the conversion of CO to CH4, with water as a by-product.

References in corpus (35)

• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• Closed-form expressions for particle relative velocities induced by turbulence
• The stickiness of micrometer-sized water-ice particles
• The structure of protoplanetary discs around evolving young stars
• Planetesimal formation starts at the snow line
• Grain Retention and Formation of Planetesimals near the Snow Line in MRI-driven Turbulent Protoplanetary Disks
• Dust size distributions in coagulation/fragmentation equilibrium: Numerical solutions and analytical fits
• Meridional flows in the disk around a young star
• Planetesimal formation around the snow line in MRI-driven turbulent protoplanetary disks
• Contemporary formation of early solar system planetesimals at two distinct radial locations
• Turbulence sets the length scale for planetesimal formation: Local 2D simulations of streaming instability and planetesimal formation
• Empirical constraints on turbulence in proto-planetary discs
• Formation of Giant Planet Satellites
• Magnetocentrifugally Driven Flows from Young Stars and Disks. VI. Accretion with a Multipole Stellar Field
• Revelations on Jupiter's Formation, Evolution and Interior: Challenges from Juno Results
• Dust-driven viscous ring-instability in protoplanetary disks
• Dust settling against hydrodynamic turbulence in protoplanetary discs
• Effects of the Planetary Temperature on the Circumplanetary Disk and on the Gap
• Efficient planet formation by pebble accretion in ALMA rings
• The Galilean Satellites Formed Slowly from Pebbles
• Meridional Circulation of Dust and Gas in the Circumstellar Disk: Delivery of Solids onto the Circumplanetary Region
• Forming pressure-traps at the snow-line to isolate isotopic reservoirs in the absence of a planet
• Snow-lines as probes of turbulent diffusion in protoplanetary discs
• A subsolar oxygen abundance or a radiative region deep in Jupiter revealed by thermochemical modelling
• Planetesimal Initial Mass Functions following Diffusion Regulated Gravitational Collapse
• The water-ice line as a birthplace of planets: Implications of a species-dependent dust fragmentation threshold
• Early stages of Galilean moon formation in a water-depleted environment
• A Self-Consistent Model for Dust-Gas Coupling in Protoplanetary Disks
• Dust-Gas Coupling in Turbulence- and MHD Wind-Driven Protoplanetary Disks: Implications for Rocky Planet Formation
• Deuterated water ice on the satellites of Saturn
• Strong clumping in global streaming instability simulations with a dusty fluid
• Early Solar System Turbulence Constrained by High Oxidation States of the Oldest Non-Carbonaceous Planetesimals
• The D/H ratio in Titan's acetylene from high spectral resolution IRTF/TEXES observations
• Callisto's Nonresonant Orbit as an Outcome of Circum-Jovian Disk Substructure