Archive for the ‘Science!’ Tag


A few years ago, the International Astronomical Union formally defined the term planet and reclassified Pluto. Instead of the last-discovered, smallest, coldest, and pretty much least of the planets, they decided Pluto is the first-discovered, innermost and one of the largest of the Kuiper Belt objects, a dwarf planet.

There was a gigantic uproar, because the media presented the change as Pluto being demoted from planet status. The truth is that Pluto wasn’t demoted, simply classified correctly.

The reclassification took Pluto from last, smallest, and least of the planet to first, possibly the largest, and innermost of a whole new class of planetary bodies — Plutoids. Just typing that word makes me happy. Plutoids: smile.

The Hayden Planetarium in New York, headed by Dr. Neil deGrasse Tyson, was the first institution to notice that Pluto doesn’t really fit in with the planets, but until the discovery of actual bodies in the theoretical Oort cloud, we didn’t have anyplace else to classify it. But Pluto looks a lot like Haumea (2004) and Makemake (2005), not to mention Eris (2003), who started the whole mess.

Eris is a dwarf planet about the same size as Pluto, but apparently about 27% more massive, which would imply it’s denser than Pluto. It’s also quite a ways farther out, about 3 times as far away from the sun as Pluto. It even has a moon, called Dysnomia.

Eris (originally dubbed Xena) was considered the 10th planet in the Solar System for a few years, until that 2006 IAU meeting, when the world’s astronomers actually defined what a planet is (about time, people). They also defined dwarf planets, Plutoids, and Plutinos (objects which have a 3:2 orbital resonance with Neptune). It was a busy meeting.

And then the hate mail started, almost all of it from the US. Dr. Tyson received so much of it he compiled it all into a book called The Pluto Files, published in 2009 — which hit the NYT extended bestseller list.

We Americans love our Pluto, king of the underworld (and Mickey’s dog!), first among the Kuiper Belt objects, with two classes of solar system objects named after it. Now isn’t that more interesting than being a lowly planet?

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