In 2006, the International Astronomical Union — the global governing body for many official astronomical endeavors, including naming and classification — took a step that had never been taken before: they officially defined the term “planet.” This contentious move, which occurred with only a tiny fraction of the membership present, and notably lacked the contributions of many leading planetary scientists and planetary astronomers, put forth three criteria for defining what gets to be a “planet” versus a non-planet. It must orbit the Sun and no other body. It must be massive enough to reach hydrostatic equilibrium: where gravity and rotation primarily determine its shape. And it must have cleared its orbit, without a substantial amount of leftover primeval material from the solar system’s formation remaining in it.…