A numerical simulation of a ‘Super-Earth’ core delivery from ∼100 to ∼8 au

Abstract

We use smoothed particle hydrodynamics simulations with an approximate radiative cooling prescription to model the evolution of a massive (∼100 au) very young protoplanetary disc. We also model dust growth and gas‐grain dynamics with a second fluid approach. It is found that the disc fragments into a large number of ∼10MJ clumps that cool and contract slowly. Some of the clumps evolve on to eccentric orbits, delivering them into the inner tens of au, where they are disrupted by tidal forces from the star. Dust grows and sediments inside the clumps, displaying a very strong segregation, with the largest particles forming dense cores in the centres. The density of the dust cores in some cases exceeds that of the gas and is limited only by the numerical constraints, indicating that these cores should collapse into rocky planetary cores. One particular giant planet embryo migrates inwards close enough to be disrupted at about 10 au, leaving a self‐bound solid core of about 7.5 M⊕ mass on a low‐eccentricity orbit at a radius of ∼8 au. These simulations support the recent suggestions that terrestrial and giant planets may be the remnants of tidally disrupted giant planet embryos.

A desert of gas giant planets beyond tens of au: from feast to famine

“…Rapid inward migration of wide separation (tens to hundreds of au) planetary mass clumps has been found in simulations by many independent groups (Mayer et al 2004;Vorobyov & Basu 2006;Boley et al 2010;Inutsuka et al 2010;Vorobyov & Basu 2010;Baruteau et al 2011;Cha & Nayakshin 2011;Machida et al 2011;Michael et al 2011;Nayakshin & Cha 2013;Malik et al 2015;Stamatellos 2015;Tsukamoto et al 2015). The defining characteristic of the process is the fact that a few Jupiter mass clumps are not massive enough to open deep gaps in their protoplanetary discs at these wide separations (Baruteau et al 2011;Malik et al 2015).…”

“…For example, grain growth may be much more rapid inside the planet than in the disc since the planet is much denser than the disc (e.g. Cha & Nayakshin 2011). If grain opacity of the planet is reduced by grain growth sufficiently, then the planet may collapse much faster (e.g.…”

“…In other studies the process is present but not analysed in detail (e.g. Boley et al 2010;Cha & Nayakshin 2011;Vorobyov 2013).…”

“…Gas clumps of planetary mass are found to migrate inward on time-scales of just a few thousand years, depending on the disc and planet masses and other parameters (Mayer et al 2004;Vorobyov & Basu 2006;Boley et al 2010;Inutsuka, Machida & Matsumoto 2010;Baruteau, Meru & Paardekooper 2011;Cha & Nayakshin 2011;Machida, Inutsuka & Matsumoto 2011;Michael, Durisen & Boley 2011). Further, the clumps may evolve not only in separation but also in mass.…”

The effect of external environment on the evolution of protostellar disks

“…Finally, it is worth noting that the disk forms only one fragment at a time, which implies that ejection of fragments into the intercluster medium due to gravitational many-body interaction in such a system is impossible (Basu & Vorobyov 2012). As many numerical studies indicate, a fragment can be driven into the disk's inner regions and probably onto the star (Vorobyov & Basu 2006, 2010Machida et al 2011a;Cha & Nayakshin 2011), ejected into the intracluster medium (Basu & Vorobyov 2012), dispersed by tidal torques (Boley et al 2010;Zhu et al 2012), or even survive and settle onto quasi-stable, wide-separation orbits (Vorobyov 2013). In Model 1, there are no accretion bursts that could be triggered by fragments migrating onto the star (see Fig.…”