Fomalhaut b
Fomalhaut b is orbiting its host star at a wide separation, where forming massive planets is difficult. To explain its current location, Fomalhaut b could have been dynamically scattered by a more massive, unseen body located at smaller separations. Several ground-based observations have searched for this hypothetical Fomalhaut "c" but have yet to find it. At very small, Solar-System-like scales any additional companions must have a mass less than thirteen times the mass of Jupiter. At slightly wider scales comparable to the locations of planets around HR 8799, any additional planets must have masses below about 2 to 7 Jupiter masses. Fomalhaut b could have formed in situ if it coalesced from small pebble-sized objects that rapidly formed into a protoplanetary core which in turn accreted a gaseous envelope.