Photos taken by the Hubble Space Telescope reveal dwarf planet Pluto has the most dynamic surface on any object in the Solar System:
The researchers note that Pluto became significantly redder in a two-year period, from 2000 to 2002.
When Hubble pictures taken in 1994 are compared with a new set of images taken in 2002 to 2003, astronomers see evidence that Pluto's northern polar region has become brighter.
Referring to the striking changes on Pluto, Professor Brown commented: "Imagine the Moon changing by that much. We're used to looking at the Moon and it being the same night after night. This thing has changed dramatically in that time.