It's been 75 years since the discovery of Pluto, but it remains a mystery. Perhaps in another 10 years some of its secrets will be revealed when a space probe gets close enough for a good look.
Pluto was quickly heralded as the ninth planet in the solar system when it was spotted Feb. 18, 1930 by Clyde Tombaugh, a young amateur astronomer at Lowell Observatory. It still holds that title today, if somewhat tenuously.
Tyson provocatively removed Pluto from his exhibit of planets five years ago, lumping it instead with a belt of comets at the edge of the solar system.
Pluto was discovered in a search for a theoretical ninth planet. The 26-year-old Tombaugh was given the assignment. Had he not been so attentive, he might have missed Pluto as he stared through an eyepiece while switching back and forth between photographic images of the night sky over northern Arizona. But he believed right away the recurring speck he saw was the elusive Planet X later called Pluto.
At the time it was discovered, Pluto was the only known object beyond Neptune in the solar system. When its moon, Charon, was spotted, that seemingly confirmed Pluto's planet status.
But astronomers also have found about 1,000 other small icy objects beyond Neptune rotating around the sun. There may be as many as 100,000 of these bodies in what's called the Kuiper Belt, said Bob Millis, director of Lowell Observatory.
Pluto, with its elongated orbit and odd orbital plane, seems to behave more like other Kuiper Belt objects than other planets, some astronomers say. They also point out Pluto is very small, smaller than Earth's moon.
In any event, the debate over what to call Pluto is mostly a question of semantics, Weaver said. And even if it somehow loses planet status, he believes it might still be the largest of the Kuiper Belt objects.
