목적격 관계대명사 문장 두 개 질문드려요

두 문장 모두 맞는지 궁금해요.
1. He has been trying to find a new planet that humans can live on. / which humans can live on. / on which humans can live. / where humans can live.
2. They were moving in a totally different direction, away from the planet that Eric had wanted to visit so badly. 두 번째 문장에서 that 대신 which를 쓸 수 있나요?