Stability of the Solar System 2:1 orbit/orbit resonance. This particular resonance has important consequences because Europa's gravity perturbs the orbit of Io. As Io moves closer to Jupiter and then further away in the course of an orbit, it experiences significant tidal stresses resulting in active volcanoes. Europa is also in a 2:1 resonance with the next satellite Ganymede. The planet Mercury is especially susceptible to Jupiter's influence because of a small celestial coincidence: Mercury's perihelion, the point where it gets closest to the Sun, precesses at a rate of about 1.5 degrees every 1000 years, and Jupiter's perihelion precesses only a little slower. At
Orbit of the Moon rearward loops in the Moon's solar orbit. Considering the Earth–Moon system as a binary planet, its centre of gravity is within Earth, about or 72.6% of the Earth's radius from the centre of the Earth. This centre of gravity remains on the line between the centres of the Earth and Moon as the Earth completes its diurnal rotation. The path of the Earth–Moon system in its solar orbit is defined as the movement of this mutual centre of gravity around the sun. Consequently, Earth's centre veers inside and outside the solar orbital path during each synodic month as the Moon