In 1930, tiny, icy world Pluto was discovered orbiting in the distant solar system. In 1978, its relatively large companion Charon was detected by ground-based observations. This year, the Hubble Space Telescope may well have detected two further members of the Pluto system.

Cold, distant, Pluto is the only planet in our Solar System which has not been visited by a spacecraft from Earth. The story goes that the legend "Pluto Not Yet Explored" on a US postal stamp depicting the tiny, mysterious world inspired a JPL employee to develop plans for a Pluto flyby.