Hydrodynamics of embedded planets’ first atmospheres – II. A rapid recycling of atmospheric gas

• DOI: 10.1093/mnras/stu2704
• Publication Date: 2015-01-25T02:00:00Z
• Authors: Chris W. Ormel; Ji-Ming Shi; Rolf Kuiper
• Keywords: Protoplanet; Gas giant

Following Paper I we investigate the properties of atmospheres that form around small protoplanets embedded in a protoplanetary disc by conducting hydrodynamical simulations. These are now extended to three dimensions, employing spherical grid centred on planet. Compression gas is shown reduce rotational motions. Contrasting 2D case, no clear boundary demarcates bound atmospheric from material; instead, find an open system where enters Bondi sphere at high latitudes and leaves through mid-plane regions, or, vice versa, when rotates sub-Keplerian. The simulations do not converge time-independent solution; atmosphere characterized time-varying velocity field. Of particular interest time-scale replenish nebular gas, treplenish. It replenishment rate, Matm/treplenish, can be understood terms modified accretion ∼|$R_\mathrm{Bondi}^2\rho _\mathrm{gas}v_\mathrm{Bondi}$|⁠, vBondi set Keplerian shear or magnitude sub-Keplerian motion whichever larger. In inner disc, replenishes shorter than Kelvin–Helmholtz contraction (or cooling) time-scale. As result, longer contract growth these terminates. Future work must confirm whether findings continue apply (thermodynamical) idealizations employed this study relaxed. But if broadly applicable, provides natural explanation for preponderance gas-rich but rock-dominant planets like super-Earths mini-Neptunes.