Feb. 18 marks the 95th anniversary of the discovery of our outermost planet-not-planet. Here's what to know about the short ...

“New Horizons shattered a major paradigm of planetary science,” says Alan Stern, the mission’s principal investigator. “Pluto ...

Clyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in Flagstaff ...

Pluto may not be a planet any more, but you still have a chance to see the distant dwarf planet at one of Michigan's ...

February 18th has been a significant date throughout history, marking a variety of events that have shaped the world. In a ...

Clyde Tombaugh discovered Pluto in 1930 at Lowell Observatory in Flagstaff. Here's how Pluto won - and lost - its planetary status.

An amateur astronomer discovered Pluto 95 years ago today. The former planet will complete an orbit in another 153 years.

Pluto was last and least of them. An icy dwarf only half the size of the United States, it was on average 3.7 billion miles from the sun. It also has a decidedly strange orbit that was highly ...

The IAU defends the definition based on Pluto’s orbit. Unlike other planets that have a more or less circular, equatorial orbit around the sun, Pluto’s is sharply inclined and highly ...

After all, what does it mean for a planet to "clear its orbit of other debris," which is the single criterion that Pluto fails? Do Jupiter's Trojan asteroids qualify as cleared? Earth has plenty ...