Archive for November 23rd, 2010

Pluto: The Biggest Dwarf Planet?

by Katie Bowell, Curator of Cultural Interpretation

New Images of Pluto from the Hubble Space Telescope

Pluto’s had a tough couple of years, hasn’t it? First Eris showed up. An object in our solar system thought to be larger than Pluto, the 2005 discovery of the dwarf planet brought Pluto’s status as a planet into question (in that regard, Eris’ name is quite appropriate: “Eris” was the Greek goddess of discord and strife). Then in 2006, the International Astronomical Union (IAU) declared that Pluto would be reclassified as a “dwarf planet.”

But now, a little bit of good news.

Last month astronomers were able to measure Eris by watching it pass in front of a star (learn more about how they measured Eris here).

By measuring how long the star disappeared behind Eris, a measurement that corresponds to Eris’ size, astronomers now believe that Eris may be no larger than 1,454 miles across. Pluto is believed to be 1,456 miles across. So is Pluto 2 miles wider? Maybe.

The size of both dwarf planets is still being explored, and with measurements so close, the winner of this size contest will likely be debated for quite some time.

However, even if Pluto is bigger than Eris, that doesn’t mean a promotion back to full planet status. Pluto still hasn’t “cleared out” its orbit, joining or consuming the smaller objects in its orbit, one of the three requirements for “planethood” established by the IAU. Pluto’s also in a neighborhood full of similarly-sized bodies, and so its dwarf status is still solid. But after five years of beat downs and demotions, if Pluto does turn out to be the largest dwarf planet, that’s still something to celebrate.

For more on the Pluto planet debate, watch PBS’s The Pluto Files.

November 2010

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