Haumea is the strangest of the dwarf planets: it spins so fast that it has been stretched into a shape like a rugby ball, its long axis roughly twice its short one. It comes with two small moons, a family of icy fragments, and a faint ring - discovered in 2017 when the ring briefly dimmed a background star.
Open the 3D Solar SystemHaumea rotates once every 3.9 hours - the fastest of any large body in the Solar System. At that rate the centrifugal effect at its equator competes with its own gravity, and the body relaxes into the elongated equilibrium shape a spinning fluid would take. The likely cause is an ancient giant collision that spun it up and blasted off the fragments that became its moons and family.
| Diameter | 1,560 km |
| Dimensions | ~2100 × 1680 × 1070 km |
| Mass | 4.000e+21 kg |
| Rotation period | 3.92 h |
| Known moons | 2 |
| Atmosphere | None detected. |
| Composition | Mostly rock under a thin shell of crystalline water ice - an ancient collision likely stripped much of its original ice mantle. |
| Discovered by | Attribution contested - Mike Brown’s Caltech team and José Luis Ortiz’s Sierra Nevada team |
| Year | 2004 |
| How | Found in 2004 survey images; first announced from Spain in 2005 |
Size and shape come from a 2017 stellar occultation combined with its lightcurve; the quoted dimensions carry uncertainties of several percent.