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!