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, and later announced in 2005 by José Luis Ortiz Moreno's team in Spain. Haumea was named after the Hawaiian goddess of childbirth and fertility in 2008, hoping it would be classified as a dwarf planet.

Haumea is thought to be the third-largest object beyond Neptune, smaller than Eris and Pluto but similar in size to Titania, a moon of Uranus. Its mass is about one-third that of Pluto and much smaller compared to Earth. Though its shape hasn't been directly seen, it is believed to be stretched out, spinning very quickly.

In 2017, scientists found that Haumea has a thin ring of material around it, the first such ring discovered around a dwarf planet or any object beyond Neptune. Scientists think Haumea's unusual shape, fast spin, bright surface, and ring system may be results of a huge collision long ago, which also created a group of objects called the Haumea family, including its two known moons, Hiʻiaka and Namaka.

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 in May 2004. They planned to tell everyone about their discovery in July 2005.

Around the same time, a team in Spain led by José Luis Ortiz Moreno found Haumea in pictures they had taken in March 2003. They told the Minor Planet Center about their discovery in July 2005.

There was some disagreement about who should get credit for discovering Haumea because the Spanish team had looked at the Caltech team's records before announcing their find. The official name for Haumea was decided later, and it used a suggestion from the Caltech team even though the Spanish team had reported their discovery first.

Name and symbol

At first, the Caltech team called Haumea "Santa" because they found it just after Christmas. The Spanish team was the first to officially report the discovery, so in July 2005 Haumea got a temporary name based on the Spanish team's pictures: 2003 EL₆₁. In September 2006, it received its official number and catalog entry as (136108) 2003 EL₆₁.

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 to discover it is on Mauna Kea in Hawaii. The name also fit because Haumea was thought to be made mostly of rock, like the earth goddess Papa, and because Haumea has many children, matching how scientists think Haumea's moons formed from pieces broken off the planet long ago.

The Spanish team's suggestion did not follow the rules for naming these kinds of objects at the time. A special symbol for Haumea exists in Unicode, but it is rarely used in science 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 be pushed out of its current path.

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 over just 3.9 hours, which tells us 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 perfectly round—it’s stretched out into a special shape. If it spun even faster, it might break apart! Scientists think this fast spin started from a big crash that created Haumea’s moons.

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 and observations in 2017 showed that Haumea has a ring that matches the path of Hiʻiaka’s orbit and Haumea’s middle area. Further math work in 2018 helped figure out how these paths are angled compared to Haumea’s middle area.

Physical characteristics

The size of objects in space can be found using how bright they look from Earth, how far away they are, and how reflective they are. Haumea is special because we can measure how much heat it gives off, which helps us guess its size. But Haumea spins very fast, which makes it stretch out into an odd shape, like a squashed ball.

We can figure out how much Haumea weighs by looking at 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 so fast—almost four times faster than a normal day on Earth—that 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 new information makes 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 noticed something special while studying Haumea. They found that Haumea has a ring around it, the first time such a ring has been seen for a dwarf planet. This ring is about 2,287 kilometers wide but only about 70 kilometers thick. It spins around Haumea very close to the planet, well inside the area where such rings can stay stable.

The ring's position lines up closely with the path of Haumea's larger moon, Hiʻiaka. Scientists think the ring's particles are in a special balance with Haumea's quick spin, which helps keep the ring in place. The ring adds just a little bit of brightness to how Haumea looks 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, sometimes called "Rudolph" at first, 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 biggest 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 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 watched 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 special views helped scientists learn about Haumea's surface.

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