NOVA

- [Narrator] A rocky world with a radius under 200 miles will tend to be oddly shaped.

While everything with a radius larger than about 200 miles is a sphere.

That is, almost everything.

Haumea, out in the depths of the solar system, is a rule breaker.

This is a world about 1300 miles long, 1000 miles wide, and less than 700 miles high pole to pole, and it isn't alone.

(tense music) Two icy moons and a thin ring of rock and ice orbit Haumea, making an unexpected and odd system.

The first like it ever discovered - Haumea was such an exciting discovery because it's large enough to be round, but for some strange reason, it's shaped like a football.

- [Narrator] So, if it's odd shape is not due to its size, then what is it?

Turns out, Haumea is spinning incredibly quickly.

This world is spending so fast it experiences an entire day and night in under four hours.

It's the fastest known rotating object in the Kuiper Belt.

- So, if this is our model of Haumea, gravity is acting to try and make it into a sphere, but because Haumea is spinning so quickly, it actually means that centrifugal forces can make it propel away from itself.

- And you'll notice that it starts to become more egg-shaped as it spins.

Ooh, cool.

It's really egg shaped now.

I'm gonna turn it off before it kills us.

(laughs) - The immensely fast rotation of Haumea spinning around is what explains the shape that we see as a stretched out oval as opposed to a perfectly round sphere.

- It's just been forced to deform into this completely football egg shape.

It has no choice.

It has to be that shape.

(ethereal music)