Haumea is a dwarf planet residing in the distant Kuiper Belt, a vast region of icy bodies beyond Neptune’s orbit. It is one of five officially recognized dwarf planets in our solar system, sharing this classification with Pluto and Eris. Discovered in 2003 and formally designated a dwarf planet in 2008, Haumea is notable for its unique characteristics, offering insights into the diverse forms celestial objects can take.
Haumea’s Distinctive Shape
Haumea has a distinctive shape, deviating significantly from the near-spherical form common among other celestial bodies of comparable size. It is highly elongated, often described as an oval, or more precisely, a triaxial ellipsoid. This unusual appearance gives it the resemblance of a rugby or American football.
Its dimensions highlight this elongation, with its longest axis measuring approximately 2,322 kilometers, a middle axis of about 1,704 kilometers, and a shortest axis around 1,138 kilometers. Its longest dimension is nearly double its shortest. For objects of its mass, a more rounded, hydrostatic equilibrium shape is expected.
The Role of Rapid Rotation
The primary reason for Haumea’s distinctive form is its exceptionally rapid rotation. Haumea completes a full spin on its axis in approximately 3.9 hours, making it one of the fastest-spinning large objects in our solar system, surpassing any other known body exceeding 100 kilometers in diameter. This fast spin generates a powerful centrifugal force that pushes material outward, particularly at Haumea’s equator.
This centrifugal force causes the dwarf planet to bulge significantly around its middle and flatten its poles. The effect is so pronounced that faster rotation could distort it further, potentially leading to a dumbbell shape or even causing it to break apart. Scientists propose this rapid spin originates from a massive impact event billions of years ago. This collision likely set Haumea into its current fast rotation and contributed to the formation of its moons and related objects.
The Force of Gravity
While rapid rotation explains the outward push on Haumea, gravity works in opposition, attempting to pull the dwarf planet into a spherical shape. For most large celestial bodies, gravity is strong enough to overcome other forces, molding them into a rounded form known as hydrostatic equilibrium. On Haumea, the powerful centrifugal force from its swift spin directly resists this inward gravitational pull, particularly along its equator.
Haumea’s elongated shape results from the interplay between these two dominant forces: gravity attempting a sphere and centrifugal force distorting it. Haumea’s extreme rotation distorts it into a triaxial ellipsoid, a shape not perfectly in hydrostatic equilibrium. Its internal composition, with an estimated density around 1.885 to 2.018 grams per cubic centimeter, also plays a role, suggesting a dense rocky core surrounded by an icy mantle. The surface gravity on Haumea varies dramatically due to this interaction, being strongest at its poles (approximately 1.076 m/s²) and significantly weaker at its equator (around 0.0126 m/s²).