Hoth, ice planet. Ideal destination for snowmobiles, bi-Athlon training, tauntaun rodeos, and ice mining.
Planet 9, is as alluring as naming your planet "Dirt". Everyone knows the name "Hoth", when I say Hoth, you think of ice, tauntaun, wampa, and snow speeders. (Maybe kissing a wookie)
All the other planets, are named for ancient gods and goddesses, the pop culture of their time of naming. If we're going to reach into "a long time ago" for a name, let's also reach "far, far, away" as would befit the planet currently understood to be furthest from our sun.