Protoplanet fast growth through atmospheric dust loading

Giant planet formation through core accretion (Pollack et al. 1996) has been history plagued with timescales problems: how to build the planet before the dissipation of the protoplanetary disk. Pebble accretion overcomes these issues by assuming that planetary cores form mainly through accreting mm to cm sized “pebbles” partially couple to the gas (Ormel & Klahr 2010; Lambrechts & Johansen 2012). Pebbles however are small enough to sublimate entirely in the envelope of the protoplanet, long before hitting the core (Podolak, Pollack, & Reynolds 1988; Venturini, Alibert, & Benz 2016), thus stalling its growth. We present a new model resolving the structure of the protoplanet’s envelope undergoing pebble accretion. The model includes processes such as pebble destruction via sublimation and sandblasting, feedback of water transport on the thermodynamic structure of the envelope, convection modelled via mixing length theory, and accurate equation of states and opacity tables. We show that even though pebbles are destroyed long before they get anywhere near the core, these solids are mostly maintained in the envelope as small dust-sized particles, allowing the protoplanet to continue growing fast via atmospheric dust and ice loading. We finally discuss the far reaching implications of this model for the mass-radius relation, chemistry, and atmospheric structure of super-Earths and mini-Neptunes.

Ali-Dib, M. And Thompson, C., 2018 (MNRAS, in revision)

Ali-Dib, M., Johansen, A., and Huang C.X., 2017 (MNRAS)

 

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