I've seen a lot of speculation that the Nine planets are our solar system (and maybe the Ninth is Pluto, which would be the not-a-planet meme, lol), although there are different theories about how they might match up. The one at the very end of Harrow sounds a lot like Earth, maybe. I saw a great idea that since John has all the Earth cultural references, maybe Gideon is blaspheming with the memes.