The vote took eight seconds. The argument has taken twenty years.
A definition built for convenience
When the International Astronomical Union settled on three criteria for planethood, the third one — clearing the neighbourhood around its orbit — was the clause that did the work. It was also the clause nobody outside the room had asked for.
We did not discover something new about Pluto. We discovered something new about the language we had been using.
What the New Horizons flyby changed
The 2015 images arrived with the kind of detail that makes categories feel small: nitrogen glaciers, a heart-shaped basin, a haze layer stacked in improbable blue bands. None of it fits the picture of an inert leftover.
The case for messiness
Planetary scientists increasingly argue for a geophysical definition — if it is round because of its own gravity and it is not a star, call it a planet. That definition is inconvenient. It is also honest.
The solar system was never tidy. Our taxonomy was.