"Although the definition may not have been very precise, it clearly categorized the bodies we knew at the time. In the 1990s, however, a remarkable series of discoveries made it untenable. Beyond the orbit of Neptune, astronomers found hundreds of icy worlds, some quite large, occupying a doughnut-shaped region called the Kuiper belt. Around scores of other stars, they found other planets, many of whose orbits look nothing like those in our solar system. They discovered brown dwarfs, which blur the distinction between planet and star. And they found planet like objects drifting alone in the darkness of interstellar space... Controversially, the new definition removes Pluto from the list of planets."