The series makes assumptions about the solar system which are outlandish by modern standards but which still seemed plausible, at least to most readers, when the stories were written. Every one of the planets of the solar system, and many of the moons and asteroids, are suitable for life; most are occupied by humanoid extraterrestrials. The initial adventures take place in the planets of the solar system. Later installments (after Captain Future invents the "vibration drive") take the hero to other stars, other dimensions and even the distant past and almost to the end of the Universe. As an example, they visit the star Deneb, who are the origin of Earth humans, as well as many other humanoids across the Solar System and beyond.