Today figures like Elon Musk and Jeff Bezos have become high-profile evangelists for private space exploration, arguing that interplanetary colonization is necessary to save humanity from extinction. Although they may have the sheen of innovation, however, these ideas are not new. A century ago a coterie of British novelists, scientists, and social theorists writing during the interwar period became preoccupied with the possibility of human extinction and believed that such a fate might be avoided by taking human civilization to the stars. Watching these intellectual developments with a wary eye, a young C. S. Lewis was increasingly skeptical of both the “extinction panic” that gripped his contemporaries and the utilitarian and environmentally exploitative imagination of planetary conquest they championed. In response Lewis penned Out of the Silent Planet (1938), a novel that imagines three sentient species that have the means to prevent their own extinction but choose not to do so. Reading Lewis’s novel as a critique of the rapacious ideologies that defined this strain of interwar speculation, this article suggests that the novel models how the humanities might effectively respond to the extinction panic and cosmic adventurism that grip our own imperiled twenty-first century.