For the first time in four billion years of life on Earth, we are preparing to step out among the stars, not just as lone astronauts or billionaire tech bros, but as a civilization. Dr Adriana Marais has dedicated her life to preparing for extraplanetary settlement, and here, she considers not just the scientific concerns of a multiplanetary existence (like terraforming and life-support systems), but also the ethical responsibilities we must carry with us as we explore new frontiers.