In the fifth or sixth book of the Foundation series they follow a map to Earth that mentions a planet with huge rings and a planet circled by a giant moon. Throughout the universe, this combination was so unique you could identify the home of humanity among trillions of planets.
It’s a weird book but I’m glad I read it.
Adams had one more short story in the Hitchhiker’s universe, but debatable whether it’s technically part of the trilogy.
Other than Adams’s radio scripts, the only other book mentioned on wiki is a book by Terry Jones (of the Pythons) based on a game that was based on the mention of the “Starship Titanic” from Life, the Universe, and Everything. I’d never heard of it before though.
I remember that. I played the game as a kid and, when I found out it was a book years later, was thrilled! After reading it, I was a bit disappointed, but it was fun.
Someone else in this is referenced what I was remembering:
Track_Shovel
Boomer Humor Doomergod
leftzero
Confused_Emus