Rather than being part of the Gang of Twelve, it may be left out in the cold …
“I think that today can go down as the ‘day we lost Pluto,’ ” Jay Pasachoff of Williams College said in an e-mail message from Prague.
Under fire from other astronomers and the public, a committee appointed by the International Astronomical Union revised and then revised again a definition proposed last week that would have expanded the number of official planets to 12, locking in Pluto as well as the newly discovered Xena in the outer solar system, as well as the asteroid Ceres and Pluto’s moon Charon.
The new definition offered today would set up a three-tiered classification scheme with eight “planets”; a group of “dwarf-planets” that would include Pluto, Ceres, Xena and many other icy balls in the outer solar system; and thousands of “smaller solar system bodies,” like comets and asteroids.
The bottom line, said Owen Gingerich, the Harvard astronomer who is chairman of the I.A.U.’s planet definition committee, is that in the new definition, “Pluto is not a planet.”
Evidently being a planet is all about being Master of Your Orbit.
The committee’s original prime criterion was roundness, meaning that a planet had to be big enough so that gravity would overcome internal forces and squash it into a roughly spherical shape. But a large contingent of astronomers, led by Julio Fernandez of the University of the Republic in Montevideo, Uruguay, has argued that a planet must also be massive enough to clear other objects out of its orbital zone. Dr. Gingerich admitted, “They are in control of things.”
So the newest resolution includes the requirement for orbital dominance as a condition for full-fledged planethood, Dr. Gingerich said. That knocks out Pluto, which crosses the orbit of Neptune, and Xena, which orbits among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.
And then there was the whole Astronomy / Geology turf war that was brewing.
Dr. Gingerich cautioned that there were many things still to be sorted out. For example, the International Astronomical Union might consider creating a special name for Pluto and other dwarf-planets, like Xena and others yet to be discovered, that dwell out beyond Neptune. If it did, he said that “plutonians” seemed like a likelier choice than the previous suggestion, “plutons.” That term was protested by geologists, who pointed out that it was already used in earth science for nuggets of molten rock
that have solidified and reached the surface.
Pluto’s being stuck into a seriously Mickey Mouse category. How Goofy.
As nice (and geeky?) as it feels to have a 12-planet system (take that, Alpha Centauri!), I can agree with the new definition’s intent. Personally, I thought it would have been important to say that a planet’s orbit not cross to within another’s (distance to Sol, regardless of inclination). This too would have knocked Pluto out of the planet camp. I suppose the new definition is very closely related, if not exact, so I’m thrilled to hear it.
Besides, it makes Pluto/Charon more closely reflect their namesakes – escort to and guardian of the outer realm/Hades/Hell.
As for UB313, why not call it Loki, the Norse god of the underworld and practical jokes (if I remember correctly). It’s appearance has sure caused a hub-bub, now hasn’t it?
Loki wasn’t so much an underworld god as a trickster (sort of). But he’d be a fine addition to the array.
As to not crossing another planet’s orbit — yeah, you could say that, but, heck, Pluto’s been doing that for quite some time now, and there hasn’t been a formal call for planet redefinition until recently.
Amusing story on NPR yesterday on another group potentially affected by Pluto’s demotion: astrologers. The interview was kind of fun, though I snorted over the assertion that astrologers have been dealing with Pluto for several thousands of years, given that it isn’t visible to the naked eye and wasn’t discovered until a century or so ago.