Pluto Neighbor Gets Downsized
Remote Sedna even smaller—but brighter—than thought, new data show.
When astronomers discovered Sedna in 2003, it was the most distant known object in the solar system, orbiting more than twice as far from the sun as Pluto. (Shortly afterward, astronomers announced the discovery of an even more distant body, now called Eris.)
Initial estimates based on optical brightness suggested Sedna was roughly two-thirds Pluto's size.
But new infrared observations have slashed Sedna's estimated size, finding the body to be just 43 percent of Pluto's width.
For the new study, András Pál, of Konkoly Observatory in Hungary, and his colleagues used the European Space Agency's Herschel Space Observatory to detect the meager heat that Sedna emits at far-infrared wavelengths.
"It's very cold," Pál said of the object. At more than
