Haumea is a dwarf planet located far beyond Neptune, known for having one of the fastest rotations in the solar system. A day on this distant world is startlingly short: Haumea completes a full rotation on its axis in approximately 3.9 hours. This rapid spin fundamentally defines the dwarf planet, influencing its physical shape and internal structure.
Haumea: A Dwarf Planet Defined
Haumea is classified as a dwarf planet and a plutoid, inhabiting the Kuiper Belt—a vast ring of icy bodies extending beyond Neptune. It is considered one of the larger objects in this distant region, estimated to be the third-largest known trans-Neptunian object after Pluto and Eris. Haumea orbits the Sun at an average distance of 43 times the Earth-Sun distance, taking 285 Earth years to complete one orbit.
The dwarf planet was officially named in 2008 after the Hawaiian goddess of childbirth and fertility. It is a member of a unique collisional family, sharing similar orbital characteristics and an icy surface with its two known moons, Hiʻiaka and Namaka. This family structure suggests that Haumea and its associated bodies were created by a massive ancient impact.
The Extremely Short Rotation Period
Haumea’s rotation period of 3.915341 hours is the fastest of any known object in the solar system larger than 100 kilometers in diameter. For comparison, a day on Earth is 24 hours, and Pluto takes more than six Earth days to rotate once. This rapid rotation makes Haumea an anomaly among large solar system bodies, which spin much slower.
Astronomers determine this speed by analyzing the dwarf planet’s rotational light curve. Since Haumea is too distant to be viewed as anything more than a point of light, scientists measure the changes in its brightness over time. As the non-spherical object rotates, the amount of light reflected changes depending on whether its long or short side faces the observer.
The observed periodic fluctuations in light intensity allow researchers to precisely calculate the rotation period. The significant brightness variations are a direct consequence of the object’s elongated shape caused by the rapid spin. This method provided the precise measurement of 3.915341 hours, confirming the exceptionally quick rotation.
How Fast Rotation Shaped Haumea
The dwarf planet’s rapid rotation is directly responsible for its unusual physical form. While most large solar system bodies are pulled into a spherical shape by gravity, Haumea spins so quickly that centrifugal force counteracts this pull. This outward force is strongest at the equator, causing the body to bulge dramatically.
Instead of being round, Haumea is stretched into a triaxial ellipsoid, resembling a stretched football or an egg. Its dimensions are unequal, with the longest axis being nearly twice as long as the shortest axis. The estimated dimensions are approximately 2,322 by 1,704 by 1,138 kilometers.
This extreme shape provides constraints on the dwarf planet’s internal composition. To maintain this distorted figure while spinning so fast, the object must be dense. Calculations suggest Haumea has a high density, implying it is composed mainly of rock covered by a thin layer of crystalline water ice. This composition is consistent with the theory that a massive collision spun up the body and stripped away much of its original icy mantle.