The Planetarium

The Planetarium is an alternate final stage introduced with Survivors of The Void. It contains the alternate final boss,. The Planetarium is accessed by clearing all the Deep Void Signals within the Void Locus, and completing it ends the game.

Completing the game through the Planetarium leads to a "Fate Unknown" message on the results screen, like obliterating in, but it has a purple icon instead of a blue one.

Environment Log
The Environment Log for the Planetarium is located in the center of the first ring, floating in empty space. When collecting it, be aware of the Voidling - the Log is past the trigger to spawn the boss, and it will likely try to attack you as you move to retrieve the logbook.