In Situ Formation of Icy Moons of Uranus and Neptune

Judit Szulágyi1,2, Marco Cilibrasi1, and Lucio Mayer1
Astrophysical Journal Letters 868, L13 Link to Article [DOI: 10.3847/2041-8213/aaeed6]
1Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
2Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093, Zurich, Switzerland

Satellites of giant planets have been thought to form in gaseous circumplanetary disks (CPDs) during the late planet-formation phase, but it was unknown whether or not smaller-mass planets such as the ice giants could form such disks, and thus moons, there. We combined radiative hydrodynamical simulations with satellite population synthesis to investigate the question in the case of Uranus and Neptune. For both ice giants we found that a gaseous CPD is created at the end of their formation. The population synthesis confirmed that Uranian-like, icy, prograde satellite system could form in these CPDs within a couple of 105 yr. This means that Neptune could have a Uranian-like moon system originally that was wiped away by the capture of Triton. Furthermore, the current moons of Uranus can be reproduced by our model without the need for planet–planet impact to create a debris disk for the moons to grow. These results highlight that even ice giants—among the most common mass category of exoplanets—can also form satellites, opening a way to a potentially much larger population of exomoons than previously thought.

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