What if homeworld has a giant spaceship in form of the 3 gem authority fused (or even homeworld is this ‘spaceship’ itself), it could be something like  green diamond or someone, as it’s green, Maybe they had a bigger one with rose combined but after the war it got destroyed, assuming that rose has a gem authority. Maybe that’s way the temple is the way it is, it’s a fusion of garnet, rose, pearl and amethyst, so it’s a new home for them.