There has been a debate going on in astronomy circles that's sort of the equivalent of Priests arguing about how many Angels can dance on the head of a pin. Should Pluto have its status as a Planet taken away? And if it is a Planet, what else has to be called a Planet too?
NPR reported today that a select panel of the International Astronomical Union has voted unanimously to recommend...
...that Pluto retain its title as a planet, and it may be joined by other undersized objects that revolve around the sun.
Some astronomers had lobbied for reclassifying Pluto because it is so tiny. And at least one major museum has excluded Pluto from its planetary display. But sources tell NPR that under a proposal to be presented at a big meeting of astronomers in Prague next week for a vote, Pluto would become part of a new class of small planets. Several more objects could be granted membership.
The full body still has to vote on the recommendation, but I'm sure this is reassurring news for
Mickey, Minnie & Donald. Although the jury's still out on
Goofy.
This whole debate is something of a semantics argument. How small is too small? How different can something be, until you have to say it is different than the others? Some have even suggested that the 9 bodies now considered Planets should be frozen and a new classification created for anything that follows...
Mercury Venus Earth
Mars Jupiter Saturn
Uranus Neptune Pluto
Part of the NPR article suggests that one of the board members who made the recommendation felt that Pluto should retain its status because of its position within our culture...
Seven experts, including a science writer and a variety of astronomers, met in Paris this past June. Under the guidance of Owen Gingerich, a historian and astronomer emeritus at Harvard, they debated for two days...
...Dava Sobel, the writer on the panel, was sympathetic to Pluto's cause. In her book The Planets, Pluto merits a chapter.
"People love Pluto, children identify with its smallness," she writes. "Adults relate to its inadequacy, its marginal existence as a misfit." Sobel has several solar system models in her house. Asked if she had torn Pluto off any of them, she said "No, Pluto is definitely there."
However, by keeping Pluto as a Planet & creating a new class, it means that other objects may fall into this new class of "
Dwarf Planets". There are other objects in the
Kuiper Belt (the area where Pluto & its 3 moons Charon, Hydra and Nix are) that would fall under the Dwarf Planet title.
2003 UB313 (nicknamed Xena) is actually larger than Pluto & has its own moon. Also,
1 Ceres, a large asteroid in the belt between Mars & Jupiter, might be upgraded under the definition proposed by the panel...
...It's unclear what astronomers will make of the new definition or how they will vote on it. Observers say the definition will have to be concise and unambiguous. What is too small to be a dwarf planet? Do moons count? What about round comets?
Some panel members say they favor counting any object which is large enough that its gravity has made it round. If the object is spinning, a small bulge would be tolerated. "We're talking about no more than four or five new planets," says Iwan Williams.
Small potato-shaped asteroids wouldn't make the cut. But Ceres, a big round asteroid between Mars and Jupiter, might qualify.
What are the major objections to Pluto being called a planet?
Size & Mass
Pluto (pictured above with its Moon Charon under our Moon) has only 4% the mass of Mercury. It's also smaller than a significant amount of the moons of the other 8 planets.
Orbit
Pluto has the most elliptical orbit of the Planets in the solar system. It's orbit actually passes into Neptune's, where Pluto is closer to the Sun at some points than Neptune.
Pluto's orbit is also inclined 17 degrees above the ecliptic plane, that the other planets have.
On the other hand? Where does it say that this makes any difference on why something should be called a Planet?