Then, in 2005, Mike Brown, a professor of astronomy at Caltech, crashed the party upon discovering Eris, similar in size to Pluto and also in the Kuiper belt, calling into question Pluto’s classification. As a result, in 2006, the International Astronomical Union (IAU) voted to adopt new requirements for planetary status—kicking Pluto out of the club and into the newly defined category of dwarf planet. (Brown expanded on his reasoning in his aptly titled memoir: How I Killed Pluto and Why It Had It Coming.) In the years since, the worlds of science and pop culture have hotly debated Pluto’s fate. Among Brown’s good-natured adversaries is Philip Metzger, a retired planetary physicist at NASA’s Kennedy Space Center, current associate scientist at the University of Central Florida, and avowed Pluto-is-a-planet believer.