In 1930, Pluto became the first Kuiper Belt object to be discovered. It was found at a time before astronomers had reason to expect a large population of icy worlds beyond Neptune. Today it's known as the "King of the Kuiper Belt" – and it's the largest object in the region, even though another object similar in size, called Eris, has a slightly higher mass. Pluto’s orbit is said to be in resonance with the orbit of Neptune, meaning Pluto's orbit is in a stable, repeating pattern with Neptune's. For every three orbits completed by Neptune, Pluto makes two orbits. In this situation, Pluto never comes close enough to Neptune to be affected much by its gravity. In fact, even though its orbit crosses Neptune's orbit, Pluto gets physically closer to Uranus than it ever does to Neptune.