In 2006, a collection of scientists known as the International Astronomical Union produced a scientific definition for a planet. This definition came with certain criteria, which Pluto failed to meet, and so Pluto was not a planet anymore.
Recently, a different group of scientists, deciding that the IAU definition was incorrect, and spurred on by public outcry over Pluto's "demotion", published an article with a different definition for planets, which now not only includes Pluto, but 109 other objects in our solar system, including our Moon!
Recently, a different group of scientists, deciding that the IAU definition was incorrect, and spurred on by public outcry over Pluto's "demotion", published an article with a different definition for planets, which now not only includes Pluto, but 109 other objects in our solar system, including our Moon!
So, which is it? Is Pluto a planet, or not? What makes a planet? Why should we care?