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

In 2006, the International Astronomical Union (IAU) voted on the definition of a planet. Famously, Pluto no longer met the ...

“New Horizons shattered a major paradigm of planetary science,” says Alan Stern, the mission’s principal investigator. “Pluto turns out to have as much complexity as Mars or Earth, so much so that I ...

Why it matters: Their new proposed definition wouldn't bring Pluto back into the planetary fold, but it could reclassify thousands of celestial bodies across the universe. How it works ...

Pluto was reclassified from a planet to a dwarf planet by the International Astronomical Union because it did not meet all three criteria of their updated definition of a planet. According to the ...