In MHD-disc winds accretion models of protoplanetary discs, the disc's midplane would maintain very low viscosity levels. Using 2D hydrodynamical simulations, we assess how a low-viscosity midplane influences the migration of multiple giant planets.
While in high viscosity, pairs of giants are often found locked in a 3:2 mean motion resonance (MMR) and migrating outwards, we find them locking in a 2:1 MMR and migrating slowly inwards. Although the migration is still inwards, we find that the pair of planets migrates slower than a single giant planet migrating in the same disc. It thus seems that multiple planetary systems could be the key to stop giant planets from becoming hot Jupiters.
Exploring this study further, we consider systems composed of four or five planets. We find that building stable resonant chains of giant planets in a low-viscosity disc is quite challenging. Nonetheless, we find that, under some reasonable condtions, a system composed of four giant planets can revert their migration and move outwards.
Once again this shows that multiplanetary dynamics and resonant chain formation is decisive in the preservation of long-period giants.