In 2012, astronomers headed by SETI chief scientist Mark Showalter used Hubble Space Telescope observations to discover two previously unnoticed moons in orbit around the dwarf planet Pluto. The two tiny satellites, measuring only 20 and 30 kilometres across, were designated “P4” and “P5”. As their designation suggests, Pluto has another three moons: Charon, Nix and Hydra. Charon, the largest (1,200 kilometres diameter), was spotted in 1978; the smaller Nix (91 km) and Hydra (114 km) were discovered in 2005.
In February, the SETI Institute started a highly popular public poll called “Pluto Rocks!” intended to find names for P4 and P5 more fitting with the plutonian system. The plan was to take two of the most popular suggestions to the International Astronomical Union (IAU) so they can (hopefully) be used as official names. It was also the IAU that, in 2006, decided to re-classify Pluto as a dwarf planet in light of the surge of discoveries of minor planetary bodies in the Kuiper Belt, the outermost region of the Solar System. Although Pluto may not (technically) be a planet any more – it was ejected from the planetary club on the grounds that it doesn’t have the gravitational clout to “clear its own orbit” – it does seem to have a rather healthy family of satellites orbiting it.
But it is the recent discovery of these small moons that have created excitement as well as alarm in the scientific community. There’s excitement for the fascinating science of this mysterious region of space, but there’s concern that the same region may turn deadly for a NASA probe currently barreling toward the plutonian system, set for a close encounter in 2015.
Welcome to the Underworld
Shortly after its discovery by US astronomer Clyde Tombaugh in 1930, British schoolgirl Venetia Burney named the mysterious world Pluto – the Latinised name for Hades, Greek god of the Underworld. This made poetic sense. The Underworld, a dark, cold, foreboding place of myth seemed to describe Pluto’s distant home perfectly – it orbits the Sun every 250 (Earth) years, 40 times the Earth-Sun distance. The “Underworld” theme stuck and decades later its family grew.
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The orbiting minions of Pluto followed the naming convention as they were discovered. Charon (discovered in 1978) was named after the mythological ferryman of Hades who transported newly deceased souls from the world of the living from the world of the dead; Nix (adapted from Nyx) is the goddess of the night (discovered in 2005); Hydra, the multi-headed serpent monster and guardian of the entrance to the Underworld (also discovered in 2005).
So, in keeping with the underworldly theme, the SETI Institute kicked off their “Pluto Rocks!” poll with a selection of mythical names of the Underworld the public could vote on: Acheron, Alecto, Cerberus, Erebus, Eurydice, Hercules, Hypnos, Lethe, Obol, Orpheus, Persephone and Styx.
One suggestion was missing, however; a fact not lost on a certain starship captain.
Pluto, the final frontier?
William Shatner, who played the famous Captain James Tiberius Kirk in the original Star Trek series and movies, pointed out that Vulcan should be added to the list. Why? Well, Vulcan isn’t only the homeworld of Kirk’s first officer Spock (Leonard Nimoy); it’s also a bona fide deity from Roman mythology – it’s the god of fire. In Greek mythology Hephaestus is Vulcan’s counterpart, something the Romans identified with.
With his celebrity clout, Shatner not only managed to get Vulcan added to the list of possible names, but when the voting ended on February 25, Vulcan was the clear winner. Cerberus came in second.
But when you start to look at the details of this frenzy of Greek-Roman gods and dwarf planet moon namings, something seems a bit “off”.
Sure, all’s fair in love and public polls, but Vulcan has little relationship with the cold, dark Underworld Pluto presides over. In fact, the deity is the god of fire! If a moon was found in orbit around Mercury, the closest planet to the Sun, “Vulcan” wouldn’t seem so odd. Pluto and its moons are very, very cold places; surely there are enough chilly deities to go around without having to use Vulcan as a substitute?
Although Shatner and the voting public are rightfully passionate about seeing a Star Trek homeworld orbiting Pluto, the suggestion will likely raise a few eyebrows at the IAU who, let’s face it, will give the naming convention a little more thought.
In an interesting twist, as argued by Skeptic Blog writer Brian Dunning, it could actually be a waste to name P4 or P5 “Vulcan”.
From Pluto to… the stars?
As we discover more worlds orbiting other stars, there is increasing pressure on the IAU to formulate a naming convention for these newly-discovered exoplanets. Currently, we’re stuck with an ad hoc naming routine that designates a letter after the already-vague naming convention for the star it’s orbiting. For example, “Kepler-37b” is so-named because the star was observed to have a planet in orbit by NASA’s Kepler space telescope. The “b” is the planet; “Kepler-37”, the star. This might make great sense for scientists cataloging exoplanetary discoveries in chronological order, but it doesn’t really inspire real star trekking dreams.
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So, Dunning brings up an interesting, and potentially critical, point. Once a celestial body or cosmic feature is named, you can’t use it again – it’s a basic (and logical, Spock) rule that avoids confusion with celestial names. Use “Vulcan” on a tiny, insignificant rock orbiting a dwarf planet in the distant reaches of the Solar System, and you can’t use it on a potentially exciting new world orbiting another star. By Dunning’s reckoning, “Vulcan” should be given to Gliese 581c, a “super-Earth” orbiting the star Gliese 581, around 20 light-years from Earth. Gliese 581c orbits the red dwarf star within its habitable zone, meaning liquid water could exist on its surface. This is exciting as liquid water is essential for life as we know it to evolve. Of course, this is a long way from saying an advanced race of Vulcans lives on its surface battling the Romulans and thinking logically, but as far as science potential goes, Gliese 581c is a little more interesting than a 20-mile wide lump of rock orbiting a dwarf planet (no offence, Pluto).
Interestingly, the second-most popular name selected in the “Pluto Rocks!” poll is Cerberus – the mythical three-headed dog that guards the gates to the Underworld. But there’s a problem… Cerberus is already used in astronomy! 1865 Cerberus is a 1.2 kilometre-wide asteroid that was discovered in 1971. Therefore, the IAU can’t use “Cerberus” as a name for Pluto’s new moon – they’d have to use the Greek version of Cerberus, “Kerberos”. This astronomical naming malarkey is a minefield!
The “Pluto Rocks!” poll certainly achieved what it set out to do – engage the public with astronomy – but it also did something more profound: it highlighted an antiquated naming system for celestial bodies that is rapidly being overtaken by a slew of astronomical discoveries. We are truly in a “golden age” of astronomy and astrophysics where groundbreaking discoveries don’t happen every decade, they happen every week.
As an aside, antiquated astronomical naming conventions are something the crowdsourcing project Uwingu is confronting while providing funding for science projects. You can log in, pay to make a nomination and pay to vote for your favourite nominated names for exoplanets. The proceeds then go toward funding science projects. Uwingu has only just kicked off, but it could be a hint of a paradigm shift in the science community.
Who are you calling “insignificant”?
Although P4 and P5 are small, as far as moons go, they are by no means insignificant from a science standpoint. Their existence is an exciting twist to Pluto’s mysterious nature – but they could also be the first hint of a very real danger.
Launched in January 2006, NASA’s New Horizons probe was sent on its 10 year journey to the farthest most reaches of the Solar System, visiting Jupiter on its way in September the same year. But its primary mission wasn’t to take a tour of the planets; it’s to fly past Pluto and its moons, making historic observations of the Pluto system in 2015. The nuclear-powered New Horizons will be the first spacecraft to see Pluto’s surface up close – a feat that has only been possible through the fuzzy pictures taken by Hubble from afar.
But as the probe ploughs through the Kuiper Belt in two years’ time, it could be in for a rough ride. The recent discoveries of Nix, Hydra, P4 and P5 suggest there may be many more small moonlets, or even an entire ring system (not unlike a miniature Saturn) hanging around in Pluto orbit. Currently, the trajectory of New Horizons’ flight will take it within the orbit of Charon around Pluto. Could that volume of space be packed with tiny obstacles? If so, there’s the potential that they could act as shrapnel as the spacecraft flies by, causing damage or even scrapping the mission all together.
As discussed by New Horizons principal investigator and Uwingu project leader Alan Stern during the February 16, 2012 Weekly Space Hangout, mission scientists are going through great pains to study the Pluto system, looking for any signs of more moons or even a debris field. Might Pluto have been the site of an ancient impact? Is it a collection of small moons and Kuiper Belt dust? Only time will tell, but emergency plans are being drawn up should the spacecraft be in jeopardy. A “bail out” trajectory is also being designated that will push the probe further away from Pluto during flyby should the danger be considered too great. In short, we don’t really know what’s hanging around in Pluto’s potentially rough neighbourhood.
So, as we debate the apparent absurdity of naming tiny, cold satellites orbiting Pluto, the fact that we have the ability to detect such tiny celestial bodies is a wonder unto itself. But the fact that we have a bold NASA spacecraft powering its way to the final frontier of the Solar System makes us realise that we should take Pluto’s moons very seriously – not because they are named after deities of Greek mythology, but because they highlight a clear danger to a historic robotic mission.
Pluto may not technically be a planet anymore, but as the “Pluto Rocks!” poll showed, it is very much alive in the imagination of the general public, a fact that will make the 2015 flyby a very special event for all mankind.
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