Haumea: The egg-shaped dwarf planet

The dwarf planet Haumea is one of the weirdest objects present out there in the Kuiper belt. It is shaped like an American football (egg-shape).

Astronomers think that Haumea was much like Pluto in its early days made up of ice and rock. Later a big object collided with it which knocked most of the surface ice and imparting a rapid spin to Haumea.

The rapid spin is the prime reason for Haumea’s unusual egg (ellipsoid) shape.

Why is Haumea called a dwarf planet and not a planet?

Same reason why Pluto is not considered a Planet.

A dwarf planet is a celestial body that:

  1. is in orbit around the Sun,
  2. has enough mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
  3. has not cleared the neighborhood around its orbit.

Haumea fails the third criteria and hence it is not a planet.

Discovery

Haumea’s discovery was a little controversial. Two teams are credited for the discovery of Haumea.

Mike Brown and his team discovered Haumea in December 2004. But they didn’t announce their discovery but published an online abstract intended to announce the discovery at a conference on September 2005.

Around the same time, Jose Luis Ortiz and his team discovered Haumea in their observatory in Spain. Ortiz emailed the Minor Planet Center about their discovery in 2005.

According to IAU whoever submits the reports first gets credited for the discovery.

Mike Brown suspected that the Spanish team had accessed his online logs to take credit for the discovery. But Ortiz later admitted that he was just checking if he has discovered a new object or not.

In 2008, IAU declared Haumea as the fifth dwarf planet but did not mention the discoverer. The location of the discovery was listed as Sierra Nevada Observatory Spain.

But the name Haumea was chosen by Mike Brown and his team. Ortiz team had proposed “Ataecina”, the Iberian goddess of Spring.

Naming

Haumea pronounced as  HAH-oo-MAY-ə was given the provisional designation 2003EL61.

Before the official name, the Caltech team used the nickname “Santa” among themselves because it was discovered just after Christmas.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was given by the Caltech team to honor the place where Haumea’s moons were discovered.

Later the two moons were named after Haumea’s daughters Hi’iaka and Namaka.

Ortiz team suggested “Ataecina” but it did not meet the IAU requirements.

Orbit and rotation

Haumea completes one rotation every 4 hours making it one of the fastest rotating objects in the solar system.

credit: Stephanie Hoover [CC0]

It has the shortest day of any object larger than 60 miles in the solar system.

Haumea takes 285 Earth years to make one orbit around the Sun.

Haumea’s rapid spin might be the reason for its weird ellipsoid shape.

Size and distance

Haumea is the fourth largest dwarf planet in the solar system behind Pluto and Makemake and Eris.

The mass of Haumea is about 32% that of Pluto.

With an average distance of 40.1 AU, it takes Sunlight about 6 hours to travel from Sun to Haumea.

Aphelion (farthest from the Sun): 51.483 AU

Perihelion (closest to the Sun): 34.952 AU

Haumea is about ¼ the radius of Earth that means three Haumea’s could fit side by side on Earth. But it only has about 1/1400th of the mass of our planet.

Surface of Haumea

On the inside Haumea is rocky but on the outside, it is covered in crystalline ice – the same ice that’s in your freezer.

Haumea's surface and inner layers

This phenomenon is strange because crystalline ice forms at above 110K, whereas Haumea’s surface temperature, is below 50K.

The Haumea is composed of mainly methane, ethane and possibly nitrogen ices, similar to that of other dwarf planets.

Haumea doesn’t have an atmosphere because its gravity is too small to hold on to an atmosphere.

It has a surface area of 6,800,000 km2 which is smaller than Australia’s 7,650,000 km2.

Haumea is also one of the brightest objects in the Kuiper belt mainly because of its icy surface.

It also has a dark red spot on its surface possibly an impact crater that may contain more minerals and organic compounds.

What it would be like to stand on the surface of the planet?

Well, considering how far it is from the Sun, the surface temperature will be around -240 degrees Celsius enough to freeze any liquid.

Haumea has a surface gravity of ≈0.401 m/s2 which is 22 times less than the Earth’s gravity. That means if you weigh 70 kilograms on Earth then you will weigh 3 kilograms on Haumea. Moving around with that much weight will be very difficult.

Rings

Yes… You heard right Haumea has rings. Jovian planets are not the only objects to have rings after all.

Haumea is the most distant object known to have rings and is the only dwarf planet that has a ring.

The ring of Haumea was only discovered in 2017 when it passed in front of a star URATI 533-182543.

The Haumea ring is about 70 km (40 miles) wide and has a radius of around 2,287 km (1421 miles).

Haumea and its rings
Credit:Tomruen [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

The ring is in the same plane with Haumea’s equator and the orbit of Hi’iaka.

The ring is in the 3:1 resonance with Haumea’s rotation, that is the ring particles make one revolution every three times Haumea rotates.

The ring also contributes to 5% of the planet’s brightness.

The real reason for the existence of the ring is not known.

Many of the mechanisms that are thought to have formed rings around the giant planets wouldn’t explain the rings around Haumea.

Part of Saturn’s rings, for instance, are made of material spewing from one of the planet’s moons, Enceladus. While Haumea has two moons of its own, they’re too small and too far from the dwarf planet to contribute to the ring.

The likeliest explanation for the existence of the ring is a large collision with another big body causing a ring of debris.

Moons of Haumea

Haumea has two moons Hi’iaka and Namaka both of which were discovered in 2005.

Hubble photoof Haumea and its two moons
Hubble photo of Haumea and its two moons
credit:Renerpho [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Hi’iaka

Hi’iaka is the outer moon and larger of the two.

It is brighter than the Namaka.

It was nicknamed Rudolph by the Caltech team.

Hi’iaka is named after the daughter of Haumea meaning goddess of the island of Hawaii and of the hula people.

It is roughly 310 km in diameter and about 1% of Haumea’s size.

Hi’iaka has a fast rotational period of 9.8 hours but a slow orbital period of 49 days. The orbit of Hi’iaka is almost circular.

The longer orbit of Hi’iaka is a consequence of both of the more distant orbit of the satellite from Haumea and the lower mass of Haumea.

Namaka

Namaka is the outer moon and smaller than Hi’iaka.

It was nicknamed Blitzen by the Caltech team.

Namaka is named after the other daughter of Haumea meaning the water spirit in Hawaiian mythology.

Namaka is about 170km in diameter.

It is about 10th the mass of Hi’iaka and 0.05% of Haumea.

Namaka is only 1.5% as bright as Haumea.

The orbital period of Haumea is 18 days and the orbit is highly elliptical, unlike Hi’iaka which has an almost circular orbit.

Astronomers believe that Haumea’s moons are part of Haumea itself. They must have been created due to an impact on Haumea in the early days of the solar system.

Will there ever be a mission to Haumea?

No such missions have been planned yet. So far only Ceres and Pluto have had a spacecraft visitor.

Conclusion

To conclude, Haumea is a very interesting egg-shaped dwarf planet hiding in the darkness of Kuiper belt waiting to be explored.

It has two moons, both with completely different orbits.

And surprisingly it also has a ring which we know very little about.

How do you think Haumea got its ring? Do let us know…

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