Pluto, god of underworld, gets busted down to demigod 5

It’s old news now, but I haven’t had a chance to comment on this monumental change in our solar system’s family tree. The International Astronomical Union (IAU) this month demoted Pluto from planet to dwarf planet, supposedly removing it from the pantheon of bodies called planets.

I told my students I’m thinking of holding a wake in Pluto’s honor. Of course, it would just be an excuse to have a party. I’m not really all that upset. Science, after all, is all about change.

And what a tiny change, at that.

Here are the facts. Way back in the early part of the 20th century, Percival Lowell, who had some pretty odd ideas about the solar system and a lot of other things, insisted on the basis of those odd ideas that there had to be a ninth planet outside the orbit of Neptune, the so-called Planet X which fringers still talk about.

After Lowell died, Clyde Tombaugh in 1930, using a blink comparator, discovered a tiny speck on his photographic plates that was eventually identified as a new planet. (Tombaugh discovered 14 other tiny specks this way, all of them asteroids.) It was quite an achievement, given the tiny size and immense distance of Pluto from Earth, and its snail-like movement across the heavens.

A contest was held to name the new find, and an 11-year-old girl, Venetia Burney, suggested the winning name: Pluto, Roman god of the underworld, whose first two letters were also Percival Lowell’s initials. With the exception of Earth, all of the other planets were named after Roman gods, so the choice was fitting. After all, Pluto was located in a very cold and dark place, as its namesake’s domain was reputed to be.

Fast forward to the early 21st century …

Our knowledge and understanding of the solar system and its constituents far surpasses what Lowell and Tombaugh could have dreamed of. Unfortunately for friend Pluto, those advances in astronomical knowledge bode ill for his membership in the Planetary Club.

Astronomers group the eight inner planets into two classes: the earth-like terrestrial planets and the Jupiter-like jovian planets. Pluto fits in neither class. Rather, Pluto and its companion moon/fellow dwarf, Charon, resemble comets in composition and structure than the terrestrials (Mercury, Venus, Earth and Mars — all rocky with metallic cores) or the jovians (Jupiter, Saturn, Uranus and Neptune — all mostly gas giants with earth-size rocky/metallic cores).

So to an astronomer, anyway, Pluto was not much of a planet. It’s small, for one thing. Its orbit is not in the same plane as the other planets, suggesting it was captured by the sun after the inner eight were formed. It’s made, presumably, of ice, dust and rock fragments. Pluto’s claim to planethood was largely based on tradition and near-religious adherence to seven decades of classroom tutelage, not on any intrinsic scientific basis.

The IAU, finally catching up to the 21st century, chose to reclassify Pluto and Charon, and a bunch of other similar objects way out there, as dwarf planets, or “plutons.” In a sense, Pluto has not really been demoted; it’s been made the archetype of a whole class of celestial objects. (Although, I have to admit, the change is a little like being sent back to manage the minors after a lifetime as a major league player.)

To the average Joe in the street, does this pedantic reclassification mean anything at all? Ultimately, no. Joe can keep on calling Pluto a planet if he likes. The astro-police are not going to haul him away for violating the IAU’s nomenclature, anymore than it will nail people for confusing Halley’s Comet with Bill Haley and the Comets.

But people get surprising emotional about this kind of stuff, although science by its nature has to change with new discoveries. Just tonight, in preparing this post, I discovered that some irate Plutonic fan had defaced the wikipedia entry on dwarf planets. I promptly edited the offending material out, but I bet it’ll be defaced again.

Maybe some people still worship the lord of the underworld. Quick! Somone call Buffy!

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5 thoughts on “Pluto, god of underworld, gets busted down to demigod

  1. Reply Dave Eaton Sep 11,2006 11:29 am

    From a scientific standpoint, I see no problem with the reclassification. The heroic work of Tombaugh makes the story compelling, and I think that the controversy will keep Pluto in our minds much more than the asteroids that were reclassified. I feel a little nostalgia for the teaching of my youth, but I’ll get over it, I think.

    Ceres is pretty round and planetary in its look, and never seemed to me to be potato-like enough to be just another asteroid, so I am satisfied with getting it and Xena (or 2003 UB313) as dwarf planets in exchange for the change in Pluto’s status.

    Now people can fight over whether to include the dwarves in the diagrams of the solar system.

  2. Reply wheatdogg Sep 13,2006 11:35 pm

    Yeah, I think it’s only we fogies who will fret over this stuff. Only experts will worry whether Pluto is a dwarf or not. Most people will call it a planet, just like most people call bacteria and viruses “germs.”

    Did you catch the editorial cartoon that has the big planets at one table, and the little planets at the little table? Pluto was fuming about being demoted.

  3. Reply Dave Eaton Sep 15,2006 12:28 am

    I missed that cartoon- I’ll look for it. It has been a bit of a buzz at work, and you’re right, the outrage is proportional to the fogie-tude of my colleagues and myself. Some of the younger crowd seem amused.

    I see that they named UB313 Eris rather than Xena. I thought Xena sounded good, and went along with the planet X motif I always heard as a kid, but Eris has an interesting spot in mythology. Goddess of discord, which fits the controversial aspect of the whole affair, and the moon (Gabrielle would have been great here) is Disnomia, the demon of lawlessness (or Lawless-ness; those crazy astronomers!)

  4. Reply eljefe Oct 23,2009 12:32 am

    There are some creationists who might differ with that perfectly valid observation, Patrick.

  5. Reply Patrick Fennimore Oct 22,2009 9:18 pm

    I enjoyed the description of the discovery, naming and classification issues regarding Pluto. I wish I had had the opportunity to have eljefe as a teacher, I know I would have enjoyed that. My comment is that this topic is a good example of how the human race has the general belief that nothing, no celestial body, no animal, plant, gravity or any thing actually exists until we (the human race) officially discovers it. However, I will assure you the thing we called Pluto, and everything else has been around long before the human race existed or started naming things. And I assure you the universe is “benignly indifferent” to our own existence.

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