Dwarf planet that are more massive than Eris are the Moon, the four Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto), one moon of Saturn (Titan), and one moon of Neptune (Triton). The others are six moons of Saturn (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus), five moons of Uranus (Miranda, Ariel, Umbriel, Titania, and Oberon), and one moon of Pluto (Charon). There are additional possibilities among TNOs, including Dysnomia orbiting Eris. Alan Stern calls these moons "satellite planets", one of three categories of planet together with dwarf planets and classical planets. The term "planemo" ("planetary-mass object") covers all three. In
Mars trilogy help them better adapt to the new worlds; to breathe thinner air (e.g. Russell), or to see better in the dimmer light of the outer planets. The books also speculate on the colonization of other planets and moons in the Solar System, and include descriptions of settlements or terraforming efforts on Callisto, Mercury, Titania, Miranda and Venus. Toward the end of the last novel, humans are taking sub-light colony ships to other stars, taking advantage of the longevity treatments to survive the trip to their destinations. A great portion of "Blue Mars" is concerned with the effects of extreme longevity