Thursday, August 24, 2006

It's official--Pluto's out

The International Astronomical Union has voted to remove Pluto from the solar system--as a planet, that is.
Meeting in Prague over the past week, IAU members rejected a proposal to increase the number of planets to 12 by including Ceres, the largest known asteroid, which orbits between Mars and Jupiter; Charon, which has been considered Pluto's moon; and 2003 UB313, an object nicknamed "Xena" that was discovered in 2005 orbiting far beyond Pluto.

Pluto is now considered a "dwarf planet" because it has an oblong orbit that overlaps with Neptune's orbit.

Ceres and Xena will also be considered dwarf planets. Charon is simply one of the "small solar system bodies."

Hubble Space Telescope in February that confirmed the existence of two new moons orbiting Pluto. Pluto and Charon are gravitationally locked so the same sides always face each other. They orbit each other every 6.3 Earth days.
Another object that is now a dwarf planet is officially named 2003 UB313, but it is better-known as "Xena." It was discovered in 2005 by Michael Brown, Chad Trujillo and David Rabinowitz from images taken in 2003 and is slightly larger than Pluto.

The name Xena comes from the TV series "Xena: Warrior Princess." Its moon is called Gabrielle, named after Xena's sidekick on the show.

The name has gained popularity because the object fits the description of astromer Percival Lowell's Planet X from the early 1900s. But some astronomers object to officially calling it Xena because the planets are supposed to be named after characters from mythology.

Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team

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