In 2005, the astronomer Mike Brown discovered a large body in the solar system that led astronomers to more stringently redefine what a planet is. As a result, they demoted Pluto, leaving only eight planets. (Brown wrote the book “How I Killed Pluto and Why It Had It Coming.”) But, in January, Brown and his colleague Konstantin Batygin published a paper in The Astronomical Journal that provided evidence of a new ninth planet, a "distant, eccentric perturber" sculpting the orbits of smaller objects with its gravitational field. Since then, other astronomers have advanced Brown’s case, arguing that the planet is also influencing the orbits of the eight known planets, including Earth. Alan Burdick, who wrote about planet nine for The New Yorker’s Web site, speaks with Brown about why he calls the planet Fatty.
This segment originally aired on January 22, 2016.