The Fascinating Story Behind How Pluto Got Its Name

In this video from our new YouTube channel, we look at the fascinating story behind how Pluto got its name.

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Bonus Facts:

  • As to whether the Disney dog really was named after the planet, that isn’t known for sure. “We thought the name [Rover] was too common, so we had to look for something else. … We changed it to Pluto the Pup … but I don’t honestly remember why,” said Disney animator Ben Sharpsteen (who also, incidentally, directed Pinocchio and Dumbo). That being said, given that the dog was given the name around the same time Pluto was major news and it sounded good as “Pluto the Pup”, it seems plausible enough that the idea for “Pluto” probably was thanks to the naming of the dwarf planet.
  • Even though Lowell died in 1916, he actually had unknowingly managed to photograph Pluto on March 19, 1915. But those at the observatory didn’t realize what the feint object was. Further, Pluto is known to have been “discovered” sixteen times without the discoverer realizing what they were looking at. The first such known discovery was on August 20, 1909 at Yerkes Observatory.
  • So given that they’d already successfully located Pluto in 1915, why did it take another 15 years to realize what they were looking at? Because after Lowell died in 1916, a 10 year legal battle ensued over an endowment Lowell had made to the observatory totaling about a million dollars ($20M today). Lowell’s widow, Constance, was suing to get that portion of Lowell’s assets for herself, rather than have it go to the observatory as Lowell had stated in his Will. Because of this legal battle, it wasn’t until 1929 when the observatory would once again look for “Planet X”.
  • While early estimates put Pluto’s mass around that of Earth and shortly thereafter, of Mars, it wasn’t until 1978 that the discovery of Charon, a moon of Pluto, allowed scientists to accurately estimate the mass of Pluto, which ended up being just 0.00218 the mass of the Earth or 0.178 of the Moon.
  • Pluto itself was finally discovered (by someone who realized what he was looking at) by a 23 year old Kansan, Clyde Tombaugh. Tombaugh had been hired by the director of the Lowell Observatory, Vesto Slipher, to find Planet X. Tombaugh took pictures of the night sky and would compare them using a “blink comparator” (basically, just a machine that would switch pictures back and forth quickly). This would allow Tombaugh to see motion of objects in the night sky. He finally nailed down what would be named Pluto thanks to three pictures taken on January 21, 23, and 29th. A process of confirming what he’d found ensued until the discovery was finally announced in the Harvard College Observatory on March 13, 1930.
  • Pluto is not the ninth most massive known object directly orbiting the Sun. That honor goes to Eris, discovered in 2005. Eris is approximately three times further away from the Sun as Pluto and is the most distant known natural object in our Solar System outside of comets. Eris itself also is known to have a moon, Dysnomia. It was partially the discovery of Eris that set aflame the argument over what should be considered a planet or not.
  • Before Eris was called Eris, the discoverers called it Xena, after Xena: Warrior Princess.
  • Venus is named after the goddess of love. It is thought this planet got its name from the fact that it is “pretty” to look at as the third most bright object in our solar system in the sky as viewed from Earth (after the Sun and the Moon). The name of the goddess, Venus, probably comes from the Proto-Indo-European root *wen-, meaning “to strive after, wish, desire, or be satisfied”.
  • Mercury is named after the god of thievery, tradesmen or commerce, and travel. It is thought that the planet probably was named such due to how quickly, relatively speaking, it travels across the sky.
  • Mars was named after the Roman god of war. It’s thought that it was labeled such based on the reddish hue of the planet, relating to blood.
  • Jupiter is named after the god of thunder and the sky, and king of the gods. It is probable that it was named such as it is the largest non-star in our solar system. In fact, Jupiter is sometimes called a failed star, though that’s somewhat of a misnomer. Jupiter is a gas giant that didn’t have enough mass to become a star. How much more mass would Jupiter need to become a star? About 60-80 times its present amount.
  • The name of the king of the gods, Jupiter, is thought to come from the Proto-Indo-European *dyeu-peter, meaning “god-father”.
  • Even though not a star, Jupiter does give off a pretty massive amount of energy. In fact, it gives off more heat than it receives from the Sun. Because of this release of heat energy, Jupiter is shrinking at a rate of about 2 cm each year. If that rate were to remain constant (it wouldn’t for a variety of reason, but it’s fun to play with numbers), Jupiter would shrink to nothing in about 7 billion years. It is estimated that Jupiter is approximately 4.5 billion years old. As you might expect from that, it was significantly more massive at its peak than it is today.
  • While you might think adding mass to Jupiter would make it bigger, it is thought that it would actually get smaller if you added significant mass, until the point where it would gain so much mass that it would become a star. For instance, in one theoretical model, the threshold for Jupiter getting bigger versus smaller is at about 1.6 Jupiter masses. Any more than that, and it would shrink as the pressure in its core increases.
  • Saturn is named after the Roman god of agriculture. Why this was chosen as the name for the planet isn’t clear.
  • Neptune was named after the god of the sea. It got its name thanks to the fact that it has a nice blue color. The name “Neptune” probably came from the Proto-Indo-European root *nebh-, meaning “cloud”, hence “moisture, wetness”.
  • Uranus is named after the very early god of the sky (and father to the Titans).
  • The tradition of naming planets after mythological gods was passed down to us after Roman names for the five extraterrestrial planets they were aware of.
  • An asteroid was named in honor of Venetia Burney, asteroid 6235 Burney. In addition to that, students who made a dust counter instrument to be included as a part of the New Horizons mission to Pluto named the instrument after Burney: The Venetia Burney Student Dust Counter. As to Venetia’s thoughts on mankind coming so far technologically from 1930 to be able to send a spacecraft to Pluto, “It is absolutely amazing, but it is paralleled by almost everything that has happened in the world, hasn’t it? I mean we have stepped so far into the future as it were since the 1920s and 1930s. It leaves one absolutely stunned. “
  • Since the demotion of Pluto from a planet to a dwarf planet, dwarf planets beyond the orbit of Neptune are now known as “plutoids”.
  • Venetia grew up to be an accountant and later a teacher of mathematics and economics and married a mathematician, Maxwell Phair, who oddly later became the head of English at Epsom College.
  • In case you’re curious, Venetia was still alive when the “Pluto is/isn’t a planet” arguments started flying and she lived to see it be demoted to a dwarf planet. She had this to say about the matter, “It’s interesting isn’t it, that as they come to demote Pluto, so the interest in it seems to have grown… At my age, I’ve been largely indifferent to [the debate]; though I suppose I would prefer it to remain a planet.”
  • Venetia died on April 30, 2009 at the age of 90.
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  • Quoting from the article: “Pluto is not the ninth most massive known object directly orbiting the Sun. That honor goes to Eris, discovered in 2005.”

    Uh-oh! This just in:
    “After [spacecraft] New Horizons measured Pluto’s diameter as 2370 km in July 2015, it was determined that Eris is slightly smaller in diameter than Pluto.”

    • Daven Hiskey

      @J.F. Gecik: Assuming the estimates on Eris aren’t equally off a titch, I don’t think we’ve ever been proven wrong in a cooler way than a machine humans sent billions of miles away beaming back said info. 🙂