Geek Trivia: Planet X marks the spot

What name for a 10th planet did authors Douglas Adams, Larry Niven, and Arthur C. Clarke coincidentally "agree" on?

All the recent ruckus about the International Astronomical Union's deliberations over the definition of a planet has warmed this Trivia Geek's recollection of the decades-old search for a 10th planet—both fictional and otherwise.

The "formal" search for a 10th planet (to abuse the term loosely) began in the early 1900s when none other than Percival Lowell—the astronomer who basically bankrolled the search for the eventual discovery of Pluto—predicted that another Jupiter-esque gas giant must reside at the edge of the solar system. Lowell's reasoning was that the only explanation for certain eccentricities in the orbits of the outer planets was another massive planetary object—its gravity tugging away at its neighbors—floating undetected in a distant orbit.

(Of course, at the time, Lowell and friends were searching for a ninth planet because no one had discovered Pluto yet. In the years since, science has discovered Pluto, anointed it as a planet, and then demoted it to non-planet status—history repeating itself, boys and girls.)

It turns out Lowell and his contemporaries just didn't have good data on Uranus and Neptune. When Voyager 2 finally did flybys of these orbs in the late 1980s, suddenly all the mathematical basis for Lowell's "Planet X" disappeared. Nonetheless, the Planet X concept was now a part of public consciousness, and an untold number of writers set about to use the "10th planet" as a plot device in their stories.

Perhaps the most famous 10th planet is Mondas, home of the Cybermen from various Doctor Who episodes. The television series Space 1999 also included adventures on a 10th planet, called Ultra. Robert A. Heinlein introduced us to a 10th planet called Kalki in his novel The Puppet Masters. Meanwhile, an innumerable number of anime and manga series have posted a cavalcade of heroes, villains, and bizarre events on a hypothetical 10th planet—all answering to various names.

Still, one name seems to appear more often than most when authors and screenwriters christen a fictional Planet X. Inspired by the traditions of naming local worlds after figures from Greco-Roman mythology, several notable science-fiction scribes—including Douglas Adams, Arthur C. Clarke, and Larry Niven—coincidentally managed to "agree" on this planetary moniker.


What name for a hypothetical 10th planet did several notable science-fiction writers—including Douglas Adams, Arthur C. Clarke, and Larry Niven—coincidentally "agree" on?

The name in question is Persephone, after the Greek goddess abducted by Hades (the Greek analogue of Pluto) to be his bride in the underworld. Niven created his Persephone for his Known Space series of books. Clarke also chose to name his 10th planet Persephone in several fictional works, most notably in his novel Rendezvous with Rama.

The Douglas Adams reference is a little more muted; in Mostly Harmless, Persephone is the official name of the 10th planet, but most folks refer to it by its nickname Rupert. (The nickname, in typical Adams fashion, somehow involved an astronomer's pet parrot.)

The selection of Persephone offers a certain amount of mythological symmetry—the planet next to Pluto would be his "bride" hidden from view in a dark realm—though it does violate the formal tradition of naming planets after Roman gods. The deviation is probably due to Persephone's Roman analogue (Proserpina) being a bit more cumbersome to speak—and certainly nowhere near as top-of-mind in the poetic or public consciousness.

Ironically, despite the preponderance of Persephones in fictional planet lore, it's unlikely that the International Astronomical Union would allow any newly discovered planet to receive the name. The IAU—the same body that had the authority to demote Pluto from its classical planetary status—explicitly forbids the reuse of names on multiple classes of celestial bodies.

For example, no asteroid can receive the same common name as a planet, simply to avoid confusion (although asteroids and moons with the same name often violate this rule). Much to the lament of fans of planet Persephone, there's already a Persephone in the solar system.

Discovered in 1899, asteroid 399 Persephone has more than a century's claim to the name. Proserpina also presents the same roadblock; scientists discovered asteroid 26 Proserpina in 1853. Despite the popularity of the suggestion, the truth of a Planet X will have to be just a little stranger than fiction—which makes for all the better Geek Trivia.

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The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best post from the assembled masses and discuss it in the next edition of Geek Trivia.

We're suspending this week's quibble for more pressing matters—plus, I just got back from vacation, and I'm still adjusting.

While all the pro-Pluto-as-planet people out there are licking their wounds from having their favorite trans-Neptunian object demoted from planethood, the rest of us can dream of a day of the discovery of a proper ninth planet in our solar system—and what Roman mythological name science should bestow on said superior orb.

Yes, it's arbitrary award time again, dear readers. In the discussion attached to this article, simply suggest a name that the IAU could use to christen a hypothetical "unknown" planet in our solar system—and then back up your choice with as much Geek Trivia as you can. I'll randomly and capriciously select the best suggestion(s) and award the members with some rarified TR swag (probably a coffee mug). No purchase necessary, not legal where void, yada yada yada—it's good to be back.

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The Trivia Geek, also known as Jay Garmon, is a former advertising copywriter and Web developer who's duped TechRepublic into underwriting his affinity for movies, sci-fi, comic books, technology, and all things geekish or subcultural.