After decades of thinking we knew a lot about the solar system, astronomers are now finding new objects at an increasing rate. Haumea is one of the most interesting.
It’s not very big – one of the smallest of the dwarf planets – but it’s definitely unusual. How much do you know about this distant dwarf?
Haumea was only discovered in 2004 and no space probe has visited it yet, so it’s taken some clever analysis to work out what it’s like. It’s well out past the orbit of Neptune and not easy to see from Earth – well out of reach of almost all amateur telescopes – so if you want to know more, read on!
Mass: 4.006×1021 kg
Equatorial Diameter: 575-718km
Known Moons: 2
Orbit Period: 284.12 years
Surface Temperature: > -223°C
How far is Haumea from the Sun?
Haumea is very far away. At its furthest, it’s 51.483 AU (7,701,747,177km, or 4,813,591,985 miles) from the Sun. Even the closest point of its elliptical orbit leaves it 34.952 AU (5,228,744,776km, or 3.267.965,485 miles) away. Its orbit overlaps Pluto’s, so sometimes Haumea is further away and sometimes Pluto is.
Can you see Haumea from Earth?
Only just, and only if you have access to a very large telescope. For amateur telescopes the answer is a definite no. Haumea is quite bright – its surface is about as reflective as fresh snow – but it’s very small and very far away.
How big is Haumea?
It’s much smaller than Pluto, with about a third of the mass. It’s also an unusual shape. Part of the definition of a minor planet is that it’s been pulled into hydrostatic equilibrium by its own gravity. Usually this means it’s roughly a sphere, probably slightly flattened by its own rotation.
Haumea is different. It’s so small and distant that even the largest telescopes can’t see what shape it is, but astronomers think they’ve calculated it from the way Haumea and its moons move. It seems to be a flattened ellipse, a bit like a giant sugared almond. It still qualifies as a dwarf planet, though.
It does have enough mass to make it spherical, but it’s still suffering the effects of a collision with another object about 100 million years ago. The same impact probably created its moons and caused its very rapid spin – Haumea rotates every 3.9 hours, faster than any other large object in the solar system.
In fact, if Haumea spun any faster it would probably break up. Its uneven shape means that a faster rotation would overcome gravity and start to stretch its shape outwards, until the stress became too much and it disintegrated.
Haumea and the Kuiper Belt
Haumea is a Kuiper Belt object, like Pluto. Most Kuiper Belt objects seem to be a mixture of ice and rock, and if they have enough gravity the rock tends to form the core inside a thick mantle of ice. It’s hard to be sure exactly what Haumea is made of, but studying its rotation and the orbits of its moons can give a lot of clues.
From what astronomers can tell, it seems to be much too dense to have a lot of ice in it. In fact it’s nearly as dense as our Moon, which is almost entirely rock. That suggests Haumea is mostly rock, with a thin layer of ice on the surface. It’s possible that most of its ice was stripped away in the collision.
The surface of Haumea
No spacecraft has investigated Haumea closely, so all we have to work on are telescope observations, but they can tell us something about the surface.
And it’s odd. By analysing the spectra of reflected light astronomers can get a good idea what it’s being reflected from, and Haumea’s surface seems to be covered in crystalline ice – that’s the sort we’re familiar with on Earth.
At temperatures as low as Haumea’s water should freeze too quickly for crystals to form, creating a different type called amorphous ice.
Are there any plans to visit?
Not right now, but astronomers have looked at how to get a probe to Haumea. It’s not easy. Even using Jupiter’s gravity to “slingshot” the craft to a higher speed it would take over 14 years for it to arrive.
More Haumea facts
- Haumea’s orbit is angled quite steeply compared to those of the planets. It’s quite similar to Pluto’s.
- It is the third brightest object in the Kuiper Belt, after Pluto and Makemake.
- Two teams of astronomers – one in Spain and one in California – both claim to have discovered Haumea first.