Pluto isn’t a planet — but it gives us clues for how the solar system formed

If you were born in the last century you might have memorized that there were nine planets in our solar system, as heard in the famous Schoolhouse Rock! song, Interplanet Janet. Upon the discovery of its existence in 1930, Pluto enjoyed decades of special status as one of the solar system's planets.

Then, in the summer of 2006, Pluto was demoted.