Uranus is unique among the giant planets: its rotation axis is tilted 98 degrees, so the planet essentially rolls on its side as it orbits the Sun. This extreme obliquity may result from a giant impact early in Solar System history. Uranus's 27 known moons include Miranda, whose bizarre cliff faces and chevron patterns suggest repeated tidal heating and re-freezing, and the larger Titania and Oberon, which show ancient cratered terrain mixed with younger resurfacing. The inner moons — Cordelia through Puck — are shepherd bodies associated with Uranus's narrow, dark ring system. All major moons orbit in Uranus's equatorial plane, sharing its extreme tilt.