Longest ever simulation of a planet in a protoplanetary disc

Ragusa et al (MNRAS 474,460: 2018) analysed the longest ever simulation of a planet in a protoplanetary disc, using the FARGO-3D code (Ben´ıtez-Llambay & Masset 2016) to follow a planet’s evolution over a record 300000 orbits. During this time the planet’s eccentricity (blue in figure below) underwent a complex evolutionary variation as it exchanged angular momentum with the disc. The simulations demonstrate that a relatively small (factor three) change in the disc mass has a major effect on the final eccentricity of the planet; the complex evolutionary pattern can be understood in terms of a superposition of precessing eccentric modes of the planet + disc system. These findings are relevant to explaining the significant eccentricity of the first hot Jupiter observed in a protoplanetary disc.

Figure 1: Eccentricity e as a function of time for light (left-hand panel) and massive (right-hand panel) case. The blue curve shows the planet eccentricity, the green curve the disc eccentricity at R = 4.7 in the light case and at R = 5 (azimuthal averages) in the massive one, while the red curve is a global measurement of the disc eccentricity starting from the AMD.

Rosotti & Juhasz (MNRAS 474,L32; 2018) proposed a novel way to probe the vertical temperature profile in protoplanetary discs from measuring the pitch angle of spiral structure in discs in both the infrared and submm. Their hydrodynamic simulations, using the PLUTO code (Mignone et al. 2007) of a planet induced spiral in a disc were post-processed with the radiative transfer code RADMC-3D and were able to demonstrate that spiral structure is significantly more tightly wound in the submm than the infrared. This finding is directly linked to the fact that submm emission traces cold mid-plane regions of the disc. This work means that multi-wavelength observations of spiral structure in real discs can be used as a `dynamical thermometer’ of disc mid-plane regions.

Winter et al (MNRAS 475,552; 2018) presented long timescale Smoothed Particle Hydrodynamical simulations using the GANDALF code (co-developped in house: Hubber et al 2018; MNRAS 473,1603) of a remarkable young stellar system whose widely spaced components are associated with extremely extended far infrared emission. These simulations demonstrated that the morphology of the emission and the kinematics of the stellar components can be explained through a dynamical history involving a previous star-disc encounter. This successful reproduction of an observed system provides some of the first evidence that young stars indeed from dynamically complex few-body systems, as suggested by star formation simulations.