It has been argued that the notion of a planet “clearing out its orbit” is too vague, so it has been made more rigorous by defining the “scattering parameter”. This parameter quantifies the ability of a planet to scatter all the smaller bodies out of its neighborhood. It is calculated as the planet’s mass squared divided by its orbital period, multiplied by another factor that describes the swarm of smaller bodies in its path (which we can consider a constant factor). In our solar system, all the planets with a scattering parameter larger than unity have mostly cleared out their orbits, whereas those with scattering parameters smaller than unity share their neighborhood with a swarm of other bodies that have not been cleared away. So it seems that this scattering parameter really works! Pluto is one of the largest bodies that has a scattering parameter less than unity, and there is a gap of over 4 orders of magnitude between scattering parameter of the weakest major planet (Mars) and the strongest dwarf planet (Pluto). This is shown in the figure, below. Doesn’t this tell us without any doubt that Pluto is not a true planet? Some people certainly think so.