Hydra is a dwarf planet in the Siam System, and is the final planetoid of the entire system. It was briefly occupied by the UNSC Sanctuary of Spring in the late 2530's when the Yagnyar were encountered. It and it's system are off limits from even the Covenant thanks to the Yagnyar. Much of the planet is unconfirmed, but the planet is around the same size as Sol Dwarf Planet Pluto.