How fast you need to move to keep in a circular orbit around another body is dictated by how far the two bodies are separated from each other. Planets closer to the Sun are orbiting faster than Earth, with Mercury traveling 1.6 times faster than Earth at 105,000mph(47.4km/s). At the other end of the spectrum is Neptune, which is traveling around the sun at only 18% of the speed of Earth at 12,200mph (5.4km/s).