While it seems simple enough, it gets fuzzy as soon as we consider other solar systems. For one thing, the scattering parameter depends not only on the planet itself, but also on the size of the star it orbits. That’s because the planet’s orbital period is shorter when the star is more massive and vice versa. Let’s consider a couple of examples. One day we will find a body the same size and mass as Saturn’s little moon Tethys but orbiting in the habitable zone of a red dwarf star. That’s not an unlikely scenario: there are billions and billions of red dwarf stars in our galaxy. It turns out that this Tethys twin will have a scattering parameter greater than unity everywhere in that star’s habitable zone. That means Tethys is a major planet when it’s at a red dwarf star.