Solar System
A general introduction to the neglected celestial bodies of humanity's home system in 40k.
Sol/Sun
It is the sun, yellow, G Class, with 5 billion years of life left under normal circumstances. General graveyard of heretics and their possessions (no pun intended).
Mercury
Venus
Luna/Moon
Used to be ruled by gene-cults with a lot of growth vats before the Emperor set off uniting the Solar System. Refusing to be annexed, big Emps sent the XVIth Legion(and co.) upon them, with the gene-cults finally saying "OK, we surrender, call off your wolves." As such, the Luna Wolves were christened.
Jupiter
A gas giant Forge World. The Imperial Navy's foremost shipyard and drydock. It only makes ships. It is a hotly contested Imperial political debate as to whether Jupiter is soverign to the Mechanicum or the Imperium. They went totally green though, the hippies.
It once had a Forge Moon, Ganymede, in orbit. It is now Perdita. Do NOT go near Ganymede.
Saturn
Base of the Solar Fleet, one of the first recruiting worlds of the Solar Auxilia, and its moon Titan is homeworld of the Grey Knights.
Uranus&Neptune
(The fact that there is a bracket here shows how much love GW has given the two planets.)
Pluto
Rogal Dorn seems to have killed Alpharius during the Battle of Pluto in the Horus Heresy.