Formation of Planetary Systems from Pebble Accretion and Migration III: The Formation of Gas Giants

Description

Previous simulations of planet formation utilizing single bodies including pebble accretion and planet migration imply that giant planets found in orbits exterior to 1 AU originate from the outer regions of protoplanetary discs (30-40 AU). Here we generalize such models to include the mutual gravity between a high number of growing planetary bodies. We investigate how the formation of planetary systems depends on the radial flux of pebbles through the protoplanetary disc and on the planet migration rate. Our N-body simulations confirm previous findings that giant planets originate from 30-40 AU when using nominal type-I and type-II migration rates and a pebble flux of approximately 100-200 Earth masses per Myr, enough to grow Jupiter within the lifetime of the solar nebula. However, planetary embryos growing interior to 30-40 AU also grow and migrate inwards to the inner system (r<1 AU) to form super Earths or gas giants, inconsistent with the configuration of the solar system, but consistent with many exoplanetary systems. Slower planetary migration rates, however, allow the formation of gas giants from embryos forming in the 5-10 AU region, which are stranded exterior of 1 AU at the end of the gas-disc phase. We identify a pebble flux threshold below which migration dominates and moves the planetary core to the inner disk, where the pebble isolation mass is too low for the planet to accrete gas efficiently. At the same time our simulations show that planetary embryos forming interior to 5 AU do not grow to gas giants, even if the migration rates are low and the pebble flux is large. The formed planets instead grow to just the mass regime of super-Earths. This stunted growth is caused by the low pebble isolation mass in the inner disc aided by the reduced pebble flux due to exterior growing planets and is thus mostly independent of the pebble flux. Additionally we show that the long term evolution of our formed planetary systems can naturally produce systems with inner super Earths and outer gas giants as well as systems of giant planets on very eccentric orbits. This talk comes as the 2nd part of a series of talks, where the 1st talk will be presented by Dr.A.Izidoro about the formation of super-Earth systems.

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