It was only in 1969 (nice) that fungi officially became its own separate kingdom.
Actually planet doesn’t have any hard set definition, we kind of just do it case by case because its damn near impossible to come up with a rigid definition that doesn’t suddenly classify some planets as moons or some moons as planets or create weird situations in which an object can switch between the two.
The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body that:
- is in orbit around the Sun,
- has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
- has “cleared the neighbourhood” around its orbit.
And in that same article:
It has been argued that the definition is problematic because it depends on the location of the body: if a Mars-sized body were discovered in the inner Oort cloud, it would not have enough mass to clear out a neighbourhood that size and meet criterion 3. The requirement for hydrostatic equilibrium (criterion 2) is also universally treated loosely as simply a requirement for roundedness; Mercury is not actually in hydrostatic equilibrium, but is explicitly included by the IAU definition as a planet
That’s not even addressing the issue of rogue planets which were ejected from their star system. Many estimates say they outnumber the stars. Obviously when a planet is ejected it doesn’t just disintegrate but by that poor definition it’s no longer a ““planet””, so it’s clearly a problematic definition.
