Wednesday, August 23, 2006


A couple of weeks ago, the cold, isolated, desolate, tiny and far away planet Pluto hit the news in a big way. An international group of astronomers was gathering in Europe to discuss the future of Pluto, discovered by Clyde Tombaugh of Kansas in 1930. The decision that these astronomers were and are tasked with will no doubt disrupt generations of basic stellar knowledge and force minor rewrites in textbooks across the nation.

Pluto, it seems, may no longer merit planetary status. It’s too small; its orbit too irregular. It’s so far away that it may in fact be just part of the Kuiper Belt, a ring of interstellar objects similar to the nearby asteroid belt between Mars and Jupiter, except that the Kuiper Belt surrounds the entire solar system.

The debate over Pluto’s planetary status is hardly a new one. The planet, named after the Roman god of the underworld (Hades in Greek), is smaller than Earth’s moon. It is so tiny that it wasn’t discovered until the 20th century, when other planets had been known for hundreds, if not thousands, of years.

Tiny Pluto, which takes 248 years to orbit the sun once, also has an irregular orbit. From 1979 to 1999, it was actually the eighth planet in our solar system, crossing over Neptune’s orbit – an every-rotation instance which won’t happen again for over 200 years. Pluto’s size and orbit made it more akin to a large asteroid or other interstellar object rather than a planetary body.

I grew up with Pluto being a solid member of our solar system family, and I suppose the fact that a Kansan discovered it makes me a little bit more affectionate towards it. Tradition and a sense of pride always turned me against efforts to oust Pluto from the planetary lineup. And it seems that a few of Earth’s most prominent astronomers agreed that Pluto should remain on par with Venus, Mars, and heavy hitters like Jupiter and Saturn.

But keeping Pluto in the system brings about other problems. What, exactly, is the definition of a planet? As astronomy and the technology to research our own home system developed, new objects were discovered – spherical, planet-like objects that were as large as or nearly as large as Pluto itself. Should they be welcomed in to the solar system with open arms, or should the definition of what makes a planet change to keep them out of the club?

Last week, it seemed that astronomers gathering at the International Astronomical Union’s (IAU) meeting in Prague were looking seriously at the former. Three new solar system objects were being considered for planetary status (or, as Pluto-and-beyond objects would be called, Plutons). Their criteria were simple: an object in the solar system that orbits the sun, is not a star or satellite of another planet, and has enough mass and gravitational pull to crush itself into a sphere. Ceres, Charon and UB-313 all fit the definition, and there are potentially dozens (if not hundreds) of other objects in the system that do as well.

Three new planets … a new term to learn – Pluton … tiny objects with irregular orbits being considered as “planetary” as my beloved Earth. I wasn’t sure how I felt about the decision the IAU seemed to be leaning toward. Textbooks would change. New “planets” could be discovered all the time. UB-313 has been nicknamed “Xena” – not after any Roman god or goddess, but Lucy Lawless’ character, the “warrior princess.”


I came to the difficult personal decision that it would be best if Pluto was booted out of our exclusive planetary club, rather than having membership opened up to any old riffraff from here to the Oort Cloud, especially if we were considering departing from the long-established tradition of using Roman and/or Greek names for our intergalactic neighbors.

And now it looks as if the IAU is coming to the same decision. Apparently astronomers found a solar system of dozens or -- God forbid -- hundreds of planets was too daunting, too complicated, and just plain wrong. An article detailing the shift in the debate from Space.com reveals possible additions to planetary requirements, including the ability to hold an atmosphere. Such a requirement kills Pluto’s hopes of remaining a planet, but it also excludes all asteroids and any trans-Neptunian objects (TNOs), saving schoolchildren the unenviable task of learning and relearning the planetary lineup of an ever-changing solar system.

Whichever way the IAU decides, the solar system is bound to change tomorrow when the final votes are cast. Little Pluto may face expulsion from the solar system after less than a century as a known planet, but interest in the icy rock is far from dwindling. The Pluto-Kuiper Express is due to arrive in 2015 and will give us the first glimpses of Pluto, which was passed over by both Voyager spacecraft that gave us breathtaking views of our system’s gas giants.

And who knows? Perhaps Pluto will have a beauty all its own. Stay tuned to find out ...

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