Fomalhaut b
The mass of Fomalhaut b, if a planet, is highly uncertain. Infrared non-detections suggest that Fomalhaut b cannot be more massive than 2 times Jupiter's mass but a lower limit on the mass depends on uncertain details for the nature of Fomalhaut b, its circumplanetary environment, and the existence of other planetary-mass bodies in the system. Models of Fomalhaut b sculpting the star's debris disk give a mass 0.5 times that of Jupiter. Models for Fomalhaut b assuming it is surrounded by a swarm of planetesimals imply that it could be much lower mass (10–100 times the mass of Earth). If Fomalhaut b is instead one of two shepherding planets that together confine the debris disk into a narrow ring, it could be anywhere between several times the mass of Mars to slightly more massive than Earth.