Separating gas-giant and ice-giant planets by halting pebble accretion

By Michiel Lambrechts, Anders Johansen, A. Morbidelli. 2014

293 citations recorded by the source corpus.

In the solar system giant planets come in two flavours: gas giants (Jupiter and Saturn) with massive gas envelopes, and ice giants (Uranus and Neptune) with much thinner envelopes around their cores. It is poorly understood how these two classes of planets formed. High solid accretion rates, necessary to form the cores of giant planets within the life-time of protoplanetary discs, heat the envelope and prevent rapid gas contraction onto the core, unless accretion is halted. We find that, in fact, accretion of pebbles (similar to cm sized particles) is self-limiting: when a core becomes massive enough it carves a gap in the pebble disc. This halt in pebble accretion subsequently triggers the rapid collapse of the super-critical gas envelope. Unlike gas giants, ice giants do not reach this threshold mass and can only bind low-mass envelopes that are highly enriched by water vapour from sublimated icy pebbles. This offers an explanation for the compositional difference between gas giants and ice giants in the solar system. Furthermore, unlike planetesimal-driven accretion scenarios, our model allows core formation and envelope attraction within disc life-times, provided that solids in protoplanetary discs are predominantly made up of pebbles. Our results imply that the outer regions of planetary systems, where the mass required to halt pebble accretion is large, are dominated by ice giants and that gas-giant exoplanets in wide orbits are enriched by more than 50 Earth masses of solids.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2835231c74d3d1236f32b662a358074415fe4f45

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Citations in the corpus

The Effect of Jupiter's Formation on the Distribution of Refractory Elements and Inclusions in Meteorites (2017, methodology): “Streaming instability is a mechanism that would collect particles in a local region in the disk into an asteroidsized chondrite parent body on short timescales, a few orbits (Johansen et al. 2007; Lambrechts & Johansen 2012; Lambrechts et al. 2014).”
Planetesimal formation near the snowline: in or out? (2017, background): “Once a protoplanet near the snowline has formed it could halt the inward-drifting pebble flux, either by accreting the pebbles (Guillot et al. 2014), or by trapping them in pressure maxima created by the newborn planet (Zhu et al. 2014; Lambrechts et al. 2014).”
Forming the cores of giant planets from the radial pebble flux in protoplanetary discs (2014, methodology): “In an accompanying paper (Lambrechts et al. 2014), we numerically determine the critical core mass for the pebble accretion model.”
The great dichotomy of the Solar System: Small terrestrial embryos and massive giant planet cores (2015, background): “bles’ Stokes number is ˝= 10 2:5. Here F is the fraction of the pebble ux which is intercepted by the outer embryo. When the outer embryo reaches 20M the ux of pebbles towards the inner embryo stops (Lambrechts et al., 2014). Thus, the inner embryo stops growing, and the simulation is stopped at thi”
Chemical enrichment of giant planets and discs due to pebble drift (2017, methodology): “Once the planetary cores become massive enough to perturb the gas surface density in the disc, the flux of pebbles from the outer disc is trapped in a pressure maximum outside the planet’s orbit and pebble accretion stops (Lambrechts et al. 2014; Rosotti et al. 2016).”
The structure of protoplanetary discs around evolving young stars (2014, background): “Such late formation of planetesimals in the outer disc could explain why Neptune and Uranus did not grow to become gas giants (Lambrechts et al. 2014; Lambrechts & Johansen 2014).”
The nature of the TRAPPIST-1 exoplanets. (2018, background): “When an embryo reaches a critical mass, it creates a pressure bump in the gas disk exterior to its orbit, which traps drifting pebbles and shuts off pebble accretion (Lambrechts et al. 2014).”
The Non-carbonaceous–Carbonaceous Meteorite Dichotomy (2020, background): “Specifically, once Jupiter’s core reached a mass of ∼ 10–20 M⊕, it would have substantially hampered exchange of material from inside (NC) and outside (CC) its orbit (Lambrechts et al. 2014).”
Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion (2017, background): “The existence of ice at the snow line depends on inward drift of small particles (Ciesla and Cuzzi, 2006), which may be blocked by an outer, ice giant-mass object (Lambrechts et al., 2014), disconnecting the condensation temperature from the presence of water (Morbidelli et al.”
Formation of planetary systems by pebble accretion and migration (2018, background): “This isolation mass can be expressed as Miso ≈ 10 × ( H/r 0.04 )3 ME, (9) which is a reasonable approximation in low-viscosity discs (Lambrechts et al. 2014).”
Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants (2018, methodology): “As soon as the planet reaches its pebble-isolation mass, the envelope of the planets is no longer heated by infalling pebbles, and gas accretion can start (Lambrechts et al. 2014).”
The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au (2019, background): “Cores stop accreting pebbles when they gravitationally perturb the surrounding disk gas so strongly that the inward drift of pebbles stalls (Lambrechts et al. 2014).”