to it was a large impetus behind demoting Pluto from planetary status in 2006.

Discovery and basic statistics

Brown's team found Sedna in 2003 as part of a larger survey of the solar system that began in 2001. Using the Samuel Oschin Telescope at the Palomar Observatory (east of San Diego) as well as Palomar's QUEST camera, the astronomers would take pictures of a tiny spot in the sky — one per hour for three hours — and see if they could find something that moved, Brown said in an explanation page about the discovery.

"The many billions of stars and galaxies visible in the sky appear stationary, while satellites, planets, asteroids, and comets appear to move. Objects in the inner Oort Cloud are extremely distant and so move extremely slowly,"of its discovery, it was at one of the closest points of its orbit to the sun, making it easier to spot.

(Image credit: NASA.)

Rise of the dwarf planets

Sedna was not the only object close to Pluto's size to be discovered in the early 2000s. Brown's team also found Quaoar, another dwarf planet candidate, and Eris. Eris was initially thought to be even larger than Pluto, prompting some to call it the solar system's 10th planet. (Later measurements showed that it may be smaller than Pluto, but at that distance and with its relatively small size, it's hard to say for sure.)

These discoveries spurred the International Astronomical Union to examine the definition of a planet in a 2006 meeting in Prague. The astronomers present voted that a planet 1)