In 2005 Professor Mike Brown and his team discovered a new dwarf planet at the edge of our solar system.
He spotted Eris in the Kuiper belt – a region of icy objects beyond Neptune.
It was more massive than Pluto and left astronomers with a dilemma: whether to add it and other larger bodies, to the list of planets or to strip Pluto of its 75-year status as the ninth planet.
Mike Brown spoke to Witness History about his discovery and the public outcry that followed.
Witness History: The stories of our times told by the people who were there.