Haumea

Haumea is a dwarf planet that orbits far beyond the planet Neptune. It was discovered in 2004 by a team led by Mike Brown at Caltech's Palomar Observatory.

Haumea is thought to be one of the larger objects beyond Neptune. It is smaller than Eris and Pluto, but similar in size to Titania, a moon of Uranus. Its mass is much smaller compared to Earth.

In 2017, scientists found that Haumea has a thin ring of material around it. This was the first ring discovered around a dwarf planet or any object beyond Neptune. Scientists think Haumea's unusual shape and fast spin may be results of a collision long ago.

History

Discovery

Main article: Controversy over the discovery of Haumea

Two groups of scientists both said they found the dwarf planet Haumea. A team from Caltech led by Mike Brown discovered Haumea on December 28, 2004, using pictures they took earlier. Around the same time, a team in Spain led by José Luis Ortiz Moreno also found Haumea. They told the Minor Planet Center about their discovery.

There was some disagreement about who should get credit for finding Haumea. The official name for Haumea was decided later.

Name and symbol

At first, the Caltech team called Haumea "Santa" because they found it after Christmas. In July 2005, Haumea got a temporary name. In September 2006, it received its official number and catalog entry.

In September 2006, the Caltech team suggested names from Hawaiian mythology for Haumea and its moons. They chose Haumea, a goddess from the island of Hawaiʻi, because one of the telescopes used is on Mauna Kea in Hawaii. The Spanish team's suggestion did not follow the rules at the time. A special symbol for Haumea exists in Unicode, but it is rarely used today.

Orbit

Haumea takes 284 Earth years to orbit the Sun. It comes closest to the Sun, called perihelion, every 35 AU (astronomical units), and its orbit is tilted at 28° compared to the planets. Haumea was farthest from the Sun, at aphelion, in early 1992 and is now more than 50 AU away. It will come to perihelion again in the year 2133.

Because of its high tilt, Haumea was harder to find early on. Most searches looked near the plane where planets orbit, but Haumea's tilted path made it harder to spot. Later searches looked in other areas and finally found Haumea. Scientists think Haumea's orbit may not stay the same forever and could one day change.

Possible resonance with Neptune

Haumea may sometimes move in a pattern related to Neptune's orbit, called a 7:12 resonance. This means for every 7 times Neptune orbits, Haumea might orbit 12 times, but this pattern does not stay the same forever. It breaks and returns over millions of years, so it is not a strong, lasting pattern.

Rotation

Haumea changes brightness a lot in just 3.9 hours, so it spins very quickly. This is the fastest spin of any big object in our Solar System. Because it spins so fast, Haumea isn’t a perfect circle—it’s stretched out into a special shape.

Right now, we see Haumea’s middle area almost edge-on from Earth. It also doesn’t line up perfectly with the paths of its ring and its farthest moon, Hiʻiaka. Studies in 2017 showed that Haumea has a ring that matches the path of Hiʻiaka’s orbit and Haumea’s middle area.

Physical characteristics

We can learn about objects in space by how bright they look from Earth, how far away they are, and how reflective they are. Haumea is special because we can measure the heat it gives off. This helps us guess its size.

Haumea spins very fast, which makes it stretch into an odd shape, like a squashed ball. We can figure out how much Haumea weighs by watching the paths of its moons. Most of its weight is in Haumea itself.

Different ways of measuring its size give slightly different numbers, but they all suggest Haumea is about as wide as a big city. Haumea spins almost four times faster than a normal day on Earth, so it has been stretched into a long, thin shape.

In 2017, when Haumea passed in front of a star, scientists got new information. This showed Haumea might be even bigger than we thought before, about as wide as Pluto at its longest point. This made scientists think Haumea might be made of different materials inside, with a rocky center covered by a thin layer of ice.

Ring

In January 2017, scientists found that Haumea has a ring around it. This was the first time a ring had been seen around a dwarf planet. The ring is about 2,287 kilometers wide but only about 70 kilometers thick. It spins very close to Haumea.

The ring's position matches the path of Haumea's larger moon, Hiʻiaka. Scientists think the ring's particles stay in place because of Haumea's quick spin. The ring makes Haumea look a little brighter from far away.

Satellites

Main article: Moons of Haumea

Two small moons circle around Haumea. They are called Hiʻiaka and Namaka. Both were found in 2005 by scientists using the W. M. Keck Observatory.

Hiʻiaka is the bigger moon. It travels around Haumea in about 49 days. It looks shiny because its surface is covered in water ice.

Namaka is the smaller moon. It orbits Haumea faster, in just 18 days, but its path is stretched out and tilted.

Collisional family

Haumea is the largest object in a group called its collisional family. This group includes objects that share similar features and paths around the Sun. Scientists think they all formed when a much larger object crashed into Haumea, breaking it apart. Besides Haumea and its moons, this group includes several other small objects.

Some scientists believe this crash also removed a lot of Haumea's icy layer. Others think the material from the crash may have formed a large moon around Haumea, which later broke apart in another crash. This family probably formed in a region called the scattered disc, where such crashes are more likely to happen. The crash that created this family is thought to have happened billions of years ago.

Exploration

The New Horizons spacecraft observed Haumea from far away in October 2007, January 2017, and May 2020. It saw Haumea from distances of 49 AU, 59 AU, and 63 AU. These observations helped scientists learn about Haumea's surface.

Future missions might visit Haumea. One idea is to send a probe that could take about 16 years to reach Haumea if launched on certain dates in 2026, 2037, and 2038. Scientists are looking at how to build such a probe, focusing on its size, power, and how it would travel through space.