Ganymede (moon) heating of the interior of Ganymede; the formation of the grooved terrain may be a result of one or more heating episodes. There are two hypotheses for the origin of the Laplace resonance among Io, Europa, and Ganymede: that it is primordial and has existed from the beginning of the Solar System; or that it developed after the formation of the Solar System. A possible sequence of events for the latter scenario is as follows: Io raised tides on Jupiter, causing Io's orbit to expand (due to conservation of momentum) until it encountered the 2:1 resonance with Europa; after that
Orbit of the Moon Orbit of the Moon The Moon orbits Earth in the prograde direction and completes one revolution relative to the stars in about 27.32 days (a sidereal month) and one revolution relative to the Sun in about 29.53 days (a synodic month). Earth and the Moon orbit about their barycenter (common center of mass), which lies about from Earth's center (about of the radius of Earth). On average, the distance to the Moon is about from Earth's center, which corresponds to about 60 Earth radii. With a mean orbital velocity of 1.022 km/s (0.635 miles/s), the Moon covers a distance approximately