Dwarf planet 2003 EL61, now known by the name Haumea (after the goddess of Hawaii), is a Kuiper Belt dwarf planet which was discovered in 2004 at a distance of 43 AU (43 times Earth's distance from the Sun), making it slightly farther out than Pluto, which is about three times as massive. Haumea is large enough that it should be spherical, compressed by its own gravity, but because of its rapid rate of rotation it is ovoid or egg-shaped.
- Discovery -
The discovery of Haumea remains contested. An American team led by Mike Brown, at the Palomar Observatory, claims that it discovered Haumea in 2004. However, a Spanish team at the Sierra Nevada Observatory, led by Jose Ortiz, claims that it actually found Haumea first, on photographs taken in 2003, though its announcement was not made until later. Critics of the Spanish team claim that they first learned of Brown's discovery, and then went back to their older data to "find" the dwarf planet themselves and claim first discovery of it. The controversy over the discovery of Haumea is an excellent example of the secretiveness and competitiveness of much of contemporary astronomy, and indeed cutting-edge scientific research in general.
The original designation, 2003 EL61, reflects the Spanish team's claim that their first images of Haumea were taken in 2003. However, the name Haumea was suggested by Brown's team. The names given to Haumea's known moons, Hi'iaka and Namaka, followed Brown's preference, as they are the names of Haumea's daughters in Hawaiian mythology.
- Orbit and Rotation -
Haumea, like all Kuiper Belt Objects, orbits the Sun beyond the orbit of the outermost planet, Neptune. In Haumea's case, this orbit ranges from about 35 to 52 times as far from the Sun as the Earth's own orbit. Astronomers calculate that at this distance it will have a year equivalent to 283 Earth-years, although, obviously, we have not yet observed Haumea through one full orbit. However, Haumea is unusual due to the length of its "day." Telescope observations indicate that it has a day of just under four hours long, making it the fastest-spinning dwarf planet or planet in the entire solar system. Haumea's extraordinarily rapid rotation has spun the dwarf planet into an ovoid or "egg" shape; normally, given its size, it should be a sphere.
In addition, astronomers have now identified two tiny moons orbiting Haumea, Hi'iaka and Namaka. All told, Haumea and its moons together are equal to less than ten percent of the mass of Earth's own Moon. The larger and outermost, Hi'iaka, is 310 kilometres across and follows a 49-day-long orbit; the smaller, Namaka, is just one-tenth the mass of its twin and follows a closer orbit, lasting just eighteen days. Both moons are credited to Brown's observatory.
- Composition -
Unlike Pluto, which is believed to be a small rocky planet covered by a large icy mantle (the New Horizons spacecraft will tell us for sure in several years' time), Haumea is actually believed to be the opposite: predominantly rock, with a thin ice surface. Since this renders it unusual among Kuiper Belt objects, astronomers believe that most of Haumea's ice must have been lost in the past, possibly in the same collisions which led to its moon system and accelerated it up to its current extraordinary rotation rate.
Careful observations of Haumea have also allowed a rough map to be sketched out. Although most of the surface is water ice, a red spot has also been identified, which probably indicates the presence of rock and organic compounds. Overall, the surface of Haumea probably roughly resembles that of Pluto, although we have never seen either dwarf planet close up.
Intriguingly, the fact that Haumea possesses two moons and also has a similar makeup to several smaller nearby objects suggests that all were formed from a single ancient collision, breaking apart a larger dwarf planet. However, this in turn suggests that Haumea ultimately comes from the scattered disk, a region beyond the Kuiper Belt. The Kuiper Belt is sparse enough that large collisions are unlikely, and close enough to Neptune's gravitational influence that families like Haumea's should have been separated rather than coming together. Ultimately, 2003 EL61-Haumea remains one of the many minor mysteries of the outer solar system.