It turns out that Pluto, the smallest and most distant planet in the solar system, isn't as lonely as we thought. Last week, astronomers announced that they had spotted two more small moons circling the pint-size planet. Before the discovery, Pluto had only one known moon, Charon (kare-uhn).
The scientific spot-light on Pluto doesn't end there. Astronomers are also trying to figure out what makes a planet a planet. Planet hunters have recently found several Pluto-size objects orbiting the Sun at even greater distances. Should these chunks of rock and ice join Saturn, Jupiter and Mars on the roll call of planets?
The size of a space object isn't the only thing that makes it a planet. Many moons orbiting known planets are bigger than the small objects that scientists are discovering. If astronomers decide that the distant, orbiting objects are truly little planets, we may add more than 20 newcomers to our solar neighborhood.
Astronomers will argue it out, and that may not be a bad thing, says Neil deGrasse Tyson, the head of the Hayden Planetarium, in New York City. "The point," Tyson told TIME "is that the solar system is a lot more interesting than just a list of nine planets."