Ganymede (moon) moon Titan, which was previously thought to have been bigger. The grooved terrain was also seen. In 1995, the "Galileo" spacecraft entered orbit around Jupiter and between 1996 and 2000 made six close flybys to explore Ganymede. These flybys are denoted G1, G2, G7, G8, G28 and G29. During the closest flyby—G2—"Galileo" passed just 264 km from the surface of Ganymede. During a G1 flyby in 1996, the Ganymedian magnetic field was discovered, while the discovery of the ocean was announced in 2001. "Galileo" transmitted a large number of spectral images and discovered several non-ice compounds on the surface of
Stability of the Solar System essentially the distance from sun to earth). These are now known as the Kirkwood gaps. Some asteroids were later discovered to orbit in these gaps, but their orbits are unstable and they will eventually break out of the resonance due to close encounters with a major planet. Another common form of resonance in the Solar System is spin–orbit resonance, where the period of spin (the time it takes the planet or moon to rotate once about its axis) has a simple numerical relationship with its orbital period. An example is our own Moon, which is in a 1:1 spin–orbit resonance