Challenges in Forming the Solar System's Giant Planet Cores via Pebble Accretion

Abstract

Though ~10 Earth mass rocky/icy cores are commonly held as a prerequisite for the formation of gas giants, theoretical models still struggle to explain how these embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of "pebbles," objects ranging from centimeters to meters in size, has been suggested as a potential solution to this long-standing problem. While pebble accretion has been demonstrated to be extremely effective in local simulations that look at the detailed behavior of these pebbles in the vicinity of a single planetary embryo, to date there have been no global simulations demonstrating the effectiveness of pebble accretion in a more complicated, multi-planet environment. Therefore, we have incorporated the aerodynamic-aided accretion physics into LIPAD, a Lagrangian code that can follow the collisional / accretional / dynamical evolution of a protoplanetary system, to investigate how pebble accretion manifests itself in the larger planet formation picture. We find that under generic circumstances, pebble accretion naturally leads to an "oligarchic" type of growth in which a large number of planetesimals grow to similar-sized planets. In particular, our simulations tend to form hundreds of Mars- and Earth-mass objects between 4 and 10 AU. While the merging of some oligarchs may allow them to grow massive enough to form giant planet cores, leftover oligarchs lead to planetary systems that cannot be consistent with our own solar system. We investigate various ideas presented in the literature (including evaporation fronts and planet traps) and find that none easily overcome this tendency toward oligarchic growth.

20 pages, 33 figures, accepted in AJ

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Cited by in corpus (19)

• Formation of planetary systems by pebble accretion and migration: How the radial pebble flux determines a terrestrial-planet or super-Earth growth mode
• Close-in planetesimal formation by pile-up of drifting pebbles
• How drifting and evaporating pebbles shape giant planets I: Heavy element content and atmospheric C/O
• Erosion and the limits to planetesimal growth
• How dust fragmentation may be beneficial to planetary growth by pebble accretion
• A Tale of Planet Formation: From Dust to Planets
• Eccentricity excitation and merging of planetary embryos heated by pebble accretion
• Rapid Formation of Jupiter and Wide-Orbit Exoplanets in Disks with Pressure Bumps
• Pebble Accretion in Turbulent Protoplanetary Disks
• A hypothesis for the rapid formation of planets
• N-body simulations of planet formation via pebble accretion II. How various giant planets form
• Building the Galilean moons system via pebble accretion and migration: A primordial resonant chain
• Establishing Dust Rings and Forming Planets Within Them
• Implications of Jupiter Inward Gas-Driven Migration for the Inner Solar System
• The interplay between pebble and planetesimal accretion in population synthesis models and its role in giant planet formation
• Can the giant planets of the Solar System form via pebble accretion in a smooth protoplanetary disc?
• On the interaction of pebble accreting embryos with the gaseous disc: importance of thermal forces
• Thermal Processing of Solids Encountering a Young Jovian Core
• Simulations of Small Solid Accretion onto Planetesimals in the Presence of Gas