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Pluto's big comeback: Why it could be reclassified as a planet

New research reveals the "trans-Neptunian object's" impressive planetary resumé

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Ken Croswell
May 29, 2014 4:45PM (UTC)
This article was originally published by Scientific American.

Scientific AmericanPoor little Pluto. In 2006 astronomers ganged up on it and voted to strip it of its planethood—but other astronomers signed a petition saying they'd ignore that vote.

Now Pluto itself seems to be fighting back. Thanks to the Hubble Space Telescope, we’ve learned that Pluto has at least five moons—pretty impressive for something that's supposedly not a planet.


And new research suggests Pluto is just what we were taught long ago: the largest world orbiting the sun beyond Neptune.

In 2005 astronomers discovered Pluto's greatest rival, Eris. It's three times farther from the sun than Pluto. And Eris was thought to be bigger than Pluto, too. But that initial estimate may have been wrong.

Other astronomers have now analyzed methane in Pluto's air. Yup, Pluto has an atmosphere—again, pretty impressive for something that's supposedly not a planet—and the methane suggests Pluto is about 1,471 miles across, versus just 1,445 miles across for Eris. The new study appears in the journal Icarus. [Emmanuel Lellouch et al, Exploring the spatial, temporal, and vertical distribution of methane in Pluto’s atmosphere]

We'll find out its exact diameter in July 2015, when NASA's first spacecraft to Pluto zips by. It'll take lots of pictures, probably find more moons and hopefully tell us whether Pluto is indeed the king of the underworld—I mean, of the solar system beyond Neptune.

Ken Croswell

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