New moons of Pluto. Hubble Space Telescope (HST) images of Pluto (white) and its large moon Charon (pale blue), and two newly discovered moons (grey). The images were taken on 15th (left) and 18th (right) May 2005, by the ACS instrument on the HST. Pluto and Charon have moved significantly with respect to each other in this time, but the outer moons, being more distant, have not moved as much. Pluto and Charon have such similar masses that they orbit a point in between them, rather than a point within the larger body, as is the case with other moons. Pluto has an eccentric orbit; its distance to the Sun varies between 4.4 and 7.4 billion kilometres.