Abstract

Recent studies on the planet-dominated regime of Type II migration showed that massive planets can migrate outwards. Using 'fixed-planet' simulations, these studies found a correlation between the sign of the torques acting on the planet (thus the direction of migration) and the parameter K' (which describes the depth of the gap carved by the planet in the disc). We perform 'live-planet' simulations exploring a range of K' and disc mass values to test and extend these results. The excitation of planet eccentricity in live-planet simulations breaks the direct dependence of migration rate on the torques imposed. By considering only the contribution to the torque due to the semimajor axis, we recover the relation between the direction of migration and K'. We then present a toy model in which the sign of planetary migration changes at a limiting value of K, through which we explore planets' migration in viscously evolving discs. The existence of the torque reversal shapes the planetary system's architecture by accumulating planets around a stalling radius, suggesting that planets pile up in the area 1-10 au, and thus disfavouring hot Jupiter formation through Type II migration in the planet-dominated regime.

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