In science, a satellite is an object that revolves around a larger body, such as a planet. There are two types of satellites referenced in astronomy. The first is a natural satellite. All of the planets except Venus and Mercury have natural satellites, also referred to as moons. Artificial satellites are man-made objects placed into orbit around another body. One example is the Hubble Space Telescope, which orbits Earth collecting images of our planet as well as images from near and deep space. There are numerous artificial satellites orbiting Earth for surveillance, research, communications, etc.
Because of its substantial mass, Jupiter has more known moons than any other planet in our solar system. Increased mass translates to increased gravitational pull. Most of Jupiter's moons are believed to be captured asteroids. Europa is among the largest of Jupiter's moons, or natural satellites.