Haumea (dwarf planet)
A stellar occultation observed on January 21, 2017 and described in an October 2017 Nature article indicated the presence of a ring around Haumea. This represents the first ring system discovered for a TNO. The ring has a radius of about 2,287 km, a width of ~70 km and an opacity of 0.5. It is well within Haumea's Roche limit, which would be at a radius of about 4,400 km if it were a sphere (not being a sphere pushes the limit out farther). The ring plane is inclined 3.2°±1.4° with respect to Haumea's equatorial plane and approximately coincides with the orbital plane of its larger, outer moon Hiʻiaka. The ring is also close to the 1:3 orbit-spin resonance with Haumea's rotation (which is at a radius of 2,285 ± 8 km from Haumea's center). The ring is estimated to contribute 5% to the total brightness of Haumea.