Consequences of an eccentric orbit for fomalhaut b

Abstract

Fomalhaut b is currently the least massive, directly imaged exoplanet candidate. New observation epochs have revealed this object to be moving on a highly eccentric orbit, which sets important new constraints. I consider scenarios where Fomalhaut b is the only object interacting with the debris disc, and ones involving an additional unseen planet. I also investigate the possibility that Fomalhaut b is merely a transient dust cloud in light of the revised eccentric orbit. I argue that the scenario best able to match the observational constraints is a super-Earth Fomalhaut b surrounded by a vast cloud of dust that is generated by a population of irregular satellites, with an undetected ∼Saturn-mass planet orbiting interior to the disc and driving the secular dynamics. Testable predictions are summarized that could differentiate between this scenario and other possibilities. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.