Below this list is a very short summary of what convinced me that Pluto is a planet.

An index of blog posts on Pluto

1. 1. A critique of the basic motive to demote Pluto: “Planet Pluto!”
   2.  A summary of several arguments: “Nine Reasons Why Pluto Is a Planet”
   3. Names of Kuiper Belt Objects, part 1: “Underworld Party in the Kuiper Belt”
   4. Names of Kuiper Belt Objects, part 2: “The Kuiper Belt Awards”
   5. The size range of planets: “Measuring Planets Like Sand”
   6. The intertwined Kuiper Belt orbits: “The Dance of the Kuiper Belt”
   7. How migration of the giant planets shaped the Kuiper Belt: “Planet Tossing and the Kuiper Belt”
   8. The composition of planets: Icy Worlds and Stars with Long Hair
   9. The geophysical definition of a planet: “How Big is a Planet?”

Summary: My Views on Pluto’s Planethood

Writing about Pluto was very educational for me.  It convinced me thoroughly that the IAU’s 2006 definition of a planet was a mistake. Here are the main three things that convinced me:

1. The smaller size of Pluto compared to some other planets is irrelevant, because there is a far wider range of sizes in many other categories of science. The largest mammal compared to the smallest mammal is a far wider range than Jupiter compared to Pluto. Are small mammals not really mammals?  Nature is filled with these examples.

2.  The IAU demoted Pluto because it did not clear its orbit. However, this rule produces absurd results when we start comparing planets at different stars. A tiny, barren rock would clear its orbit in the habitable zone of a red dwarf star, but a world just like Earth with oceans and possibly life would not clear its orbit in the habitable zone of a star just a little bigger than the sun. Therefore, the big Earth-like world is not a planet, but the tiny barren rock is.  Doubtless there are millions of worlds just like these examples in our galaxy.  This absurdity does not promote scientific discourse in comparative planetology. In fact, it hinders discourse and so it has the exact opposite effect that a scientific classification system is supposed to have.

3. The original motive for demoting Pluto derives from the archaic belief that planets “reign in their orbits” as gods (hence the names of the planets). But when science overthrows an archaic idea, we must embrace the science instead of the archaic idea. Planets don’t generally reign in their orbits. That’s only a characteristic of the inner solar system where there is inadequate space for the more complex intertwined orbits that must exist in the outer solar system. Our archaic belief in god-like planets was the result of not having good telescopes.