• The New Horizons satellite approaches Pluto. (SBS)Source: SBS
In honour of the documentary Chasing Pluto, which captures the New Horizons satellite's nine-year, three-billion mile journey to photograph Pluto up close, we’re celebrating the dwarf planet formerly known as a planet. Here’s a primer…
Ian Cuthbertson

4 Dec 2015 - 12:12 PM  UPDATED 4 Dec 2015 - 12:22 PM

Pluto and its moon Charon are in a constant, face-to-face dance of discomfort.

Yes, the icy planet -- or dwarf planet, as it was reclassified in 2006 -- is still mighty enough to keep its main moon, Charon, tidally locked. This means the moon and the planet always show each other the same face. It’s a bit like the one you wear when you ask your boss for a raise, and the one she wears when she says “no”. It also means that, just like our moon, Charon has a dark side. Go on then, insert the Pink Floyd or Star Wars joke of your choice here.

Pluto’s year is long. Game of Thrones hiatus long.

Here on Earth so much of what we live for and celebrate is annual. Christmas, New Year, public holidays, birthdays. So unless the inhabitants of Pluto are longer lived than Star Trek’s Vulcans, it could be a long time between birthdays – 248 Earth years, to be precise. But if intelligent life can survive in an atmosphere of nitrogen, methane, and carbon monoxide, at an average temperature of -229C then gaps between New Year’s Eves would be the least of it.


Pluto’s orbit is tilted and intersects the orbit of Neptune. Thankfully, it won’t go near Uranus (I’m so sorry).

If you look at the orbits of the other eight planets, at considerable distance from each other they go in plain circles around the sun. Pluto, on the other hand, acts as if someone slapped the side of the celestial pinball machine. Its orbit is elliptical and just plain weird. For this reason, Pluto’s orbit intersects the orbit of Neptune and at times Pluto is closer to the sun. Astronomers say they will never collide but imagine the heat and fireworks in the sky if they did.


Charon’s siblings are ne’er do well vagabonds who play by their own rules.

Astronomers tend to use the phrase “sister moon” but Charon’s siblings Hydra, Nix, Styx and Kerberos definitely behave like delinquent brothers. Nix doesn’t even rotate, rather it tumbles through space like that epic foetus in 2001: A Space Odyssey. Styx, meanwhile, orbits Pluto three times for every orbit Hydra completes.


Size matters, but just barely.

Proportionally, Charon is gigantic by comparison with our own moon, at roughly half the size of Pluto. Pluto is about one tenth the size of the Earth and carries about .002 per cent of its mass. It could, theoretically, park itself like a tumour on the Earth between Mexico and Canada. Similarly, the delinquent moons could fall into the Aegean and nobody would notice. At least the potato shaped Hydra (43 km wide) and Kerberos (30.5 km in diameter) sound as if they belong there.


A day is a week long. Don’t act like you’re not impressed.

If you think the long years are weird, the days on Pluto are weirder still. The sun rises and sets once each Earth week. This is apparently because the planet spins on its axis much more slowly than Earth does. It also spins in the opposite direction which is bound to be deeply disorienting for any human visitors with diurnal difficulties to begin with.


There is water, water everywhere. Yes, even there. And there. Yes and there.

You might die of hypothermia on Pluto but chances are you’d never know thirst. Despite its tiny size, there is three times as much water on Pluto than in all the oceans on Earth. The planet is 33 per cent water in the form of ice, and 67 per cent rock. Percentages of easy listening, heavy metal, and alternative rock aren’t available.


It’s so far away from the sun we’ve used ALL CAPS for dramatic effect.

Because of its elliptical orbit, distances from the sun to Pluto can only be expressed as averages. So on average, Pluto is about 40 times further from the sun than the Earth, worked out from an average of 39 and 50. In hard kilometres, that's between 4.4 and 7.4 BILLION of them from the sun. No wonder it takes sunlight five and half hours to get there.


Are you just some regular Earth loser? On Pluto, you could be Superman.

If you thought those Apollo astronauts had it easy lumbering about on the moon, consider this: a person weighing 100kg on Earth would weigh just 7kg on Pluto. My, wouldn’t that be good for those joint aches and pains caused by being overweight. If you happen to be quite fit like Superman, whose powers were bequeathed by lower gravity on Earth than his native Krypton, you’d probably be able to fly on Pluto. Up, up and away!


It’s not named after the Disney dog. (Okay, you probably did know that. Or maybe you didn’t. Nevertheless, here we are.)

It really depends who you ask. Though Pluto was officially named on March 24th, 1930, some say there was a vote for the name, with choices of Minerva, Cronus, and Pluto. Others say the planet was named by 11-year-old Venetia Burney of Oxford, England, who suggested to her grandfather that the distant world should be named for the Roman god of the underworld. Still others say a man appeared on a flaming pie, and said: “call the damn thing Pluto and be done with it.”


Clearer facts and a broader picture will be available in the documentary Chasing Pluto on Monday, 7 December at 7.30pm on SBS and On Demand after broadcast.