Our idea of a planet may need fixing. Currently, scientists define a planet as a nearly round celestial body that orbits our sun and has strong enough gravity to move objects like asteroids out of its path. But this definition has problems, including that it leaves out any planets that orbit stars outside our solar system.

That’s why astronomers in the U.S. and Canada recently proposed a new definition: a celestial body with a mass between that of Mercury (our solar system’s smallest planet) and 13 times that of Jupiter (our largest planet) that orbits any star. Pluto, which was once considered a planet but downgraded in 2006, is still too small to make the cut.