The Mathematics of Whether Pluto is a Planet

In April 2026, Pluto came up at a Senate hearing, and the old argument was back. This paper takes the IAU’s 2006 definition apart one criterion at a time. Pluto orbits the Sun, and it is round. The third test, clearing its orbital neighborhood, is the one it fails, and the paper measures that failure three independent ways. All three agree, by orders of magnitude.

The argument does not end with a verdict on Pluto. The word “planet” is being asked to do two jobs, one about what a body is and one about what it does to everything around it, and the paper makes the case for giving those jobs two separate words.

I wrote this in April 2026, before the series started, and corrected it in September 2026.