Regular moons around planets have small circular orbits and low inclinations. These objects probably formed in an early circumplanetary disk of gas and dust that surrounded the planet during formation. Some of the regular moons, such as the Galilean moons around Jupiter and Titan around Saturn, are larger than the planets Mercury or Pluto. When Galileo discovered these four giant moons orbiting Jupiter in 1610 he determined that the Earth was not the center of the Universe. The smaller inner satellites of the giant planets have such weak gravity that they preferentially lose material from the bombardment of micro meteoriods swirling around a planet. This creates the dust rings observed around the various giant planets.