The Search For Planet 9

Remember when you were in school and you learned that there were 9 planets in the solar system?
Then there was all that unpleasantness with Pluto in 2006. 
Well good news! Thanks in part to our next guest you can essentially forget that that ever happened. Sort of...
Mike Brown is Richard and Barbara Rosenberg Professor of Planetary Astronomy at the California Institute of Technology and one of the scientists at the forefront of the search for Planet 9.