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Basic Information

Pluto is a minor planet in our Solar System. Pluto is merely one of the hundreds of trans-neptunian objects orbiting our sun, and neither the largest nor the most massive of the plutoid dwarf planets. Thus it doesn't technically fit the definition of a planet, even though it was officially labeled as one during the period between its discovery in 1930 and its reclassification in 2006.

Discovery and History

Pluto was discovered in 1930 by the Lowell Observatory, which was studying photos of space attempting to locate the hypothetical Planet X - instead they found Pluto, which is much smaller than the nonexistent planet for which they were searching. At the time of its discovery, Pluto was quite the media sensation. The public was asked suggest names, and eventually it was named for the Roman God of the Dead, deemed fitting because it was so cold and dark. Before the year was out, the name of the new planet had been also bestowed on the new animated pal of Mickey Mouse. Prior to its eventual reclassification, Pluto was considered the 9th planet of our system.

The official reclassification by the International Astronomical Union in 2006 was very controversial, upsetting conventions that the most recent generations of astronomers grew up with. The IAU's argument essentially amounts to the fact that you were to call Pluto a planet, you'd probably have to grudgingly accept that Ceres (dwarf planet) and Eris (dwarf planet) and a few others have at least as much in common with the other planets as Pluto does. Largely it comes down to semantics and qualifications - depending on how you define "planet" you could argue that our solar system includes 8, 13, or possibly hundreds of planets. Exactly 9, however, is a hard number to justify given the objects we know of.

Physical Details

Pluto is a small ball of ice and rock about a fifth as massive as our moon (and 1/5,000th the mass of the Earth). It has four moons of its own: Charon (moon), Nix (moon), Hydra (moon), and S/2011 P 1. The largest of these moons, Charon, is just over half the diameter of Pluto itself. Pluto and Charon could be considered a double planet as they actually both revolve around a center of mass that is between them. The other moons are much smaller and further away from Pluto.

Pluto's roughly 248-year orbital path is very different from that of the planets. It has a highly elliptical orbit, at a sharp angle to the rest of the rest of the solar system. Most of the time it is much further from the Sun than Neptune is, but for occasional cycles of 14 to 20 years it will be closer to the Sun than that large planet is. Because Pluto is so very light in mass, its orbit is sped up and slowed down somewhat chaotically as it passes through the Solar System. It is a stable orbit, but one that is increasingly hard to predict over great amounts of time.

Because small dark objects with unusual orbits are difficult to detect from Earth, there remains a significant possibility that there may be three or four dozen vaguely similar plutoids in our Solar System that we have yet to discover.


Pluto was discovered in the 1930s, in the midst of Prohibition, at about the same time as the rise of Fascism and the Great Depression. It is thus astrologically associated with corruption, abuse of power, and rebirth-via-destruction. It is also said to influence business, investigation, mining, and surgery.


Not terribly long after it was discovered, H.P. Lovecraft once said that the planet Yuggoth in his Cthulhu Mythos was actually Pluto. Later writers expanding on the Mythos have defined Yuggoth as a much larger planet (with an equally eccentric orbit) that has eluded mundane observation.


1. Wikipedia on Pluto - and I scoured a number of other Wikipedia pages for various parts of the above.

Game and Story Use

  • In a Pulp genre, Steampunk, or Historical Campaign set around 1930, the discovery of Pluto (and the media sensation around it) can serve as a nice bit of set dressing and flavor to help establish the era.
  • In a setting where the Gods Need Prayer Badly (and/or one where the Gods are essentially Mythagoes or Egregores), the reclassification of Pluto could be a non-trivial event that shifts the balance of the universe! Does the scientific consensus on Earth reflect the politics on Mount Olympus, or is it the other way around? Can a deity be crowned, promoted, or stripped of their power by a bunch of egghead astronomers?
    • Returning to the 1930s, the same sort of twists might happen when Pluto was discovered. Did the naming of the planet reflect a new prominence for the King of the Dead, or did it merely reveal some scheme that had been exposed by the other gods already? What exactly is Pluto's relationship to the Mafia, World War II, or Walt Disney?
  • In a setting where space travel is trivial, Pluto might have some sentimental or ironic value, and might be colonized or claimed by someone with an agenda. Perhaps it's considered a bit of inside joke amongst the Hipsters of future to hang out on a planet that's officially not, so someone builds a bar, nightclub, resort or spaceport there.
    • Pluto is so far from the sun it's really really dark and cold. So you'll need some pretty good technology make it even remotely habitable.
  • The first manned expedition to travel as far out as Pluto discovers Lovecraft was right. The claustrophobic, perilous environs of a deep space exploratory craft would be a great place to unleash a bizarre eldritch abomination (frozen in the Plutotian ice, perhaps?), mind-blowing mystery, or nauseating bit of body horror.
  • If Pluto-like objects are indeed common, this really expands the size of planetary systems. So many science fiction settings assume just a handful of planets per star, but there could be hundreds. Only really high-tech civilizations would be able to make any of them habitable , but asteroid mining and similar notions could at least cash in on the abundant resources at the edge of a star system.
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