Haumea
A dwarf planet shaped like a football by its four-hour spin, with two moons and a ring found in 2017, orbiting about 43 au from the Sun once every 285 years.
At a glance
- Status
- IAU dwarf planet[2]One of the five the International Astronomical Union recognizes, with Ceres, Pluto, Makemake and Eris
- Size
- About 1,740 km across at the equator, about one seventh the width of Earth[1]NASA's rounded figure; the occultation measurement below gives the true, elongated shape
- Shape
- An elongated ellipsoid whose longest axis is at least 2,322 km[3]A stellar occultation in 2017 measured an outline of 1,704 by 1,138 km; the density is at most about 1.9 g/cm³
- Orbit
- About 43 au from the Sun on average, once every 285 years[1]Sunlight takes 6 hours to reach it
- Orbit shape
- 34.7 to 51.4 au from the Sun, tilted 28.2° to the plane of the planets[4]Semi-major axis 43.1 au
- Day
- About 4 hours[1]One of the fastest-rotating large objects in the solar system; the spin is what stretches it
- Moons
- Two, Hi'iaka (outer) and Namaka (inner)[1]Both discovered in 2005 and named for the daughters of the Hawaiian goddess Haumea
- Ring
- One, about 2,287 km from the center and about 70 km wide[3]It blocks about half the starlight passing through it; the first ring found around a Kuiper belt object
Timeline
- March 7, 2003Discovered[1]Sierra Nevada Observatory, Spain, the location the IAU lists; two teams claim the discovery from observations in 2003 and 2004
- January 26, 2005Hi'iaka discovered[4]Mike Brown, Antonin Bouchez and the Keck Observatory adaptive-optics teams
- November 7, 2005Namaka discovered[4]The same teams at the Keck Observatory
- 2017Ring discovered[1]Announced after astronomers watched Haumea pass in front of a star
Haumea is a dwarf planet in the Kuiper belt unlike any other: it spins so fast, once every four hours, that its own rotation has stretched it into the shape of a football.[1] It is one of the five dwarf planets the International Astronomical Union recognizes, with Ceres, Pluto, Makemake and Eris.[2] NASA gives its equatorial diameter as about 1,740 km, about one seventh the width of Earth, but its true shape is an elongated ellipsoid, and it has two moons and a ring.[1][3]
A disputed discovery
Two teams claim credit for finding Haumea, citing observations made in 2003 and 2004.[1] The IAU's gazetteer lists the discovery location as the Sierra Nevada Observatory in Spain on 7 March 2003, with no official discoverer.[1] The object was first designated 2003 EL61 and nicknamed Santa by one of the teams; it is named for the Hawaiian goddess of fertility and childbirth, and its moons for her daughters.[1][4]
Orbit
Haumea orbits the Sun at an average distance of 43 astronomical units, about 6.5 billion km, once every 285 years; sunlight takes 6 hours to reach it.[1] JPL's catalogue gives a path from 34.7 to 51.4 astronomical units, tilted 28.2 degrees to the plane of the planets.[4]
Shape, surface and interior
On 21 January 2017 Haumea passed in front of a star, and observers at several sites timed the star's disappearance.[3] The outline they measured was 1,704 by 1,138 km, and because of the body's rotation its longest axis is at least 2,322 km.[3] The same measurement gave an upper limit on its density of about 1,885 kg per cubic meter, lower than earlier estimates, and a surface that reflects about half the sunlight falling on it.[3] Astronomers believe Haumea is made of rock with a coating of ice; very little is known about its surface or atmosphere, and it is not thought to have a magnetic field.[1]
Two moons and a ring
Haumea's two moons were both discovered in 2005.[1] Hi'iaka, the outer moon, was found on 26 January and Namaka, the inner one, on 7 November, by Mike Brown, Antonin Bouchez and the Keck Observatory's adaptive-optics teams.[4] The 2017 occultation also revealed a ring, the first known around a Kuiper belt object: about 2,287 km from Haumea's center and about 70 km wide, blocking about half the light that passes through it.[3][1] The ring lies in the plane of Haumea's equator and of Hi'iaka's orbit, close to where a particle would circle Haumea three times for every rotation of the body.[3]
What is not yet known
Haumea has never been visited by a spacecraft. Its measured shape is not what a uniform body spinning in equilibrium would take, so its interior is not understood; how it came to spin so fast, and what its surface is made of in detail, remain open as well.[3][1]
Sources
- [1]NASA, Haumea — science.nasa.gov, retrieved November 5, 2026
- [2]NASA, Pluto & Dwarf Planets — science.nasa.gov, retrieved November 5, 2026
- [3]arXiv (Nature 550, 219–223, 2017), The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation — doi.org, retrieved November 5, 2026
- [4]NASA/JPL Small-Body Database, 136108 Haumea (2003 EL61) — ssd.jpl.nasa.gov, retrieved November 5, 2026
Related
- What is a dwarf planet?The definition that made Pluto a dwarf planet in 2006, the five the IAU recognises, why the list grows so slowly, and the candidates waiting to join it.
- The Kuiper belt and beyondThe ring of icy worlds past Neptune, the scattered disk and the Oort cloud beyond it, how many objects are known, and how new ones are found.
- PlutoThe largest known body in the Kuiper belt and the first dwarf planet, counted as the ninth planet from 1930 to 2006 and visited by New Horizons in July 2015.
- MakemakeA dwarf planet slightly smaller than Pluto and the second-brightest object in the Kuiper belt, with frozen methane on its surface and a moon found in 2016.
- ErisThe dwarf planet about the size of Pluto whose discovery in 2005 led to Pluto's reclassification; it orbits about 68 au from the Sun once every 557 years.
- QuaoarA dwarf-planet candidate about 1,110 km across on a nearly circular orbit beyond Pluto, with a moon, Weywot, and two rings where none were expected.