In the universe of the book, the planet we know as Mars does not exist. In its stead is the planet Minerva, which is larger and closer to the Sun, allowing it to have a breathable atmosphere, and has an extensive ecology including an intelligent species. Minervan Fauna (including the sentient Minervans) are radially symmetrical, which means that they have eyes spaced all around their bodies, can see in all directions at once and have no "back".