<human>:  Who discovered the planet 9?
<bot>: The discovery of Planet 9 was made by a team of astronomers led by Mike Brown. They used the Hubble Space Telescope to look for objects beyond the orbit of Neptune. They found a large object that was not a planet, but they could not determine if it was a dwarf planet or a comet. They named it Planet 9 because it was the ninth object they found.