Haumea (dwarf planet)

136108 Haumea (symbol )^[1] is a dwarf planet in the Solar System. Its discovery was announced in 2005 by astronomers Michael E. Brown, Chad Trujillo and David Rabinowitz of the United States, and J. L. Ortiz of Spain. It was classified as a dwarf planet on September 17, 2008.^[2] 136108 Haumea is a Trans-Neptunian object, because it orbits the Sun after Neptune. It has two known moons, Hiʻiaka and Namaka. 136108 Haumea is special because of its very short day and odd shape. It turns once on its axis every four hours. This quick turning has caused 136108 Haumea to be shaped like an ellipsoid. It was the fifth discovered dwarf planet.^[3]

The object was originally nicknamed 'Santa' as it was discovered shortly after Christmas.^[4] In 2008, the International Astronomical Union gave it the proper name 136108 Haumea, after a Hawaiian god of childbirth and fertility.^[3]

A stellar occultation observed on January 21, 2017, and described in an October 2017 Nature article, indicated the presence of a ring around 136108 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 136108 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 136108 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 136108 Haumea.

• NASA visualization of the orbit Archived 2005-07-30 at the Wayback Machine
• Entry at Mike Brown's Planets, explaining how he discovered it
• Michael Brown's webpage