Pluto: Trials and Tribulations of Naming Hell’s Moons


Pluto, King of the Underworld, was forever followed by Charon, his loyal ferryman who transported the souls of the dead to Hell. This is what I grew up thinking as I looked at pictures of the distant dwarf planet in my astronomy books and space magazines. Hell was an icy place, which was fitting, since Dante’s centre of hell is a massive icefield.

Recently we discovered there was more than one moon circling Pluto. This, too, makes sense to me, as here’s a lot to Hell. Charon traverses the river Styx, and across the other side of Hell lies the river Acheron, and then there are a multitude of creatures and beings – harpies, the Hydra, Kerberos, for example.


In 2005, two more moons were discovered. The first was named Nix, goddess of Darkness and the mother of Charon. If you’re a mythology buff and have noticed the odd spelling, never fear. There is already an asteroid called by the original Greek spelling, Nyx, so to avoid confusion the lovely people at the IAU have chosen the more Egyptian form of the name.

The second moon discovered in 2005 was named Hydra, the nine-headed serpent and foe of Hercules. A fitting underworld inhabitant.

Then two more moons were discovered last year. This time, their naming procedure went to public vote. The first moon was named Kerberos with little trouble – Kerberos being the beast that guards the Gates of Hell, the three-headed dog (Greek mythos sure does like things with multiple heads, eh?). But the second one’s naming procedure was quite contentious. The options are here, and the results are here. Can you spot the problem?

To explain more fully, the International Astronomical Union (IAU) has a certain naming procedure for celestial groups. Each group must contain names that are relevant to a specific area of a particular mythology. The golden rule is that mythologies and groupings should not be mixed; a name has to refer to a character or element that has substantial connection to the area.

In Pluto’s case, the mythology is ancient Greek, and the grouping is the Underworld. Most of the names suggested in the poll link into this, except for Vulcan, who is Roman and who is connected with volcanoes, fire and blacksmiths. Vulcan lends his name to the island of Vulcano, which is where the word volcano comes from. The wider region of Sicily and Southern Italy was his domain, and his smithy was said to lie beneath Mount Etna. Although his Greek cognate is the hearth god Hephaestus, the Mount Etna thing actually connects Vulcan to an older myth, from when the Greeks first visited Sicily. They believed the destructive god Typhon was locked up beneath Mount Etna to quietly steam and, occasionally, try to escape, causing lava to threaten the villages on Etna’s slopes. As Roman mythology took over from the Greek, Vulcan superseded Typhon in Sicily and the personality of the fire god beneath the mountain became more carefree, more vibrant.

The point is, not only is Vulcan in the wrong mythos, but he has very little to do with the underworld. It’s almost an insult to the mythical character to connect him to the underworld, as he hated being cooped up. He is more akin to a free-roaming, free-burning fire spirit. It’s so far from Pluto’s icy, dark world.

However, the poll results went in Vulcan’s direction. See, if you don’t already know, Vulcan refers to both a race of beings and a planet in the Star Trek world. This choice was endorsed by William Shatner and Leonard Nimoy, key actors in the Star Trek franchise. Predictably, the fans went wild and Vulcan was the leading choice. My spirits sank.

But then, to my delight, the IAU overruled the Vulcan decision, because it did not meet all of the requirements as outlined above. It’s now called Styx, which makes it particularly fitting when Charon crosses its path. Woohoo!

There was another interesting element to their decision to overrule the result. One of the other requirements is that the name cannot refer to anything currently in existence. That’s why Nix is spelled Nix and not Nyx, as there is already an asteroid called Nyx. In the case of Vulcan, it was deemed too similar to the ‘real’ Vulcan, and I say that with quotation marks because the planet Vulcan was something that people thought was very real in the 18th Century. Allegedly a planet between Mercury and the Sun, Vulcan is now thought to have just been a trick of the eye and can be explained by a number of things, which I will delve into in more detail in a later blog post.

Anyway, I’m glad the IAU got the last choice. I get very picky about groupings that don’t have storified causality to link them. Having Vulcan in this list was like reading a fanfiction where the writer inserts their own headcanon character with little regard for the canon plot and little skill at weaving them into the narrative.

IF, however, someone creates a story that manages to canonically link Vulcan to Pluto’s domain (I would suggest, since he sort of shares his home with the Greek god/monster Typhon, he could somehow be returning to the Ancient world underground after being locked up underneath Mount Etna…) then I might accept it. But it would have to be good.

On a side note, I am disappointed that Acheron, Tartaros and Thanatos got such low votes. What might this mean? Well, certainly that those who voted are more interested in Star Trek than in mythology, which I suppose is nothing new. But I was a bit disappointed to see the Star Trek celebrity endorsements of a name which has so little to do with Pluto. I suppose it would be better if Star Trek used mythos cleverly,  like the ever-impressive Stargate does.

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