As the shuttle heads for home, its main contribution to space science, the Hubble Space Telescope, has discovered a new moon orbiting Pluto. P4, as the new body is known, shows up as a smudge in these Hubble images taken earlier this summer. With a diameter of just 13-34 kilometres, it’s little smaller than Pluto’s moons Nix and Hydra, which Hubble also discovered back in 2005. But P4 is a pipsqueak compared to Pluto itself (diameter of about 2,300 km) or its largest moon Charon (~1,000 km).

Do all these moons mean that Pluto can be a planet now? No.

Credit: NASA, ESA, and M. Showalter (SETI Institute)