It Depends On What the Word "Planet" Means

9 Planets? 12? What’s a Planet, Anyway?, NY Times

“The solar system is much more complicated now, astronomers say, than in 1930 when Clyde Tombaugh added Pluto to the inventory of wandering lights circling the Sun. In addition to Earth, Mars, Venus, Jupiter, Saturn, Mercury, Neptune, Uranus and Pluto, schoolchildren now learn that there are also comets and asteroids bumping about in the night. But there are also the Oort cloud, a hypothesized halo of cometary bits hibernating in deep, deep space, and the Kuiper Belt, a ring of icy bodies beyond Neptune’s orbit. Not mention the dozens of moons circling the planets.”