The Solar System is a device that will illuminate any sort of darkness inside a cave's sublevels. This way, you can see things that are very far from you in a cave. This does not refer to where we live, it really means a system that produces solar or light energy. To get this device, you will need to retrieve the Stellar Orb, which can be found on the final sublevel of the Subterranean Complex, inside the Man-at-Legs there.