Fomalhaut b
In order for Fomalhaut b to be detectable at optical wavelengths, it must have an emitting area much larger than the physical size of a planet, a fact further strengthening the case that what we see as Fomalhaut b is not light coming from a planetary atmosphere. A circumplanetary ring system is large enough to scatter enough starlight to make Fomalhaut b visible only if it has a radius between 20 and 40 times that of Jupiter's radius. A spherical cloud of dust with a radius of can make Fomalhaut b visible. Fomalhaut b appears as an unresolved point source in the highest-quality data (at 0.6 μm) which would suggest that its projected emitting area cannot be larger than about 0.25 AU, about 1/4th of the Earth–Sun distance. However, it may be resolved at slightly longer wavelengths and in the most recently analyzed HST data, which would indicate that its emitting area is larger.