Pluto shows changing colour in new images

NASA released the most detailed set of images ever made of Pluto on Thursday, revealing that the dwarf planet looks significantly different from the last time such pictures were taken.

A map of Pluto was constructed from multiple images from the Hubble Space Telescope taken from 2002 to 2003.

NASA said the changes in colour and brightness took place during the period from 2000 to 2002, and most likely show that sheets of nitrogen ice are shifting and sublimating, transitioning from a solid directly to a gas.

As Pluto moves into a new season in its 248-year-long cycle, more sunlight is shining on the north pole, causing nitrogen ice there to sublimate and refreeze on the south pole.

The molasses colour of the pictures is thought to be due to ultraviolet radiation from the sun breaking up methane, which leaves behind charcoal black and reddish residue.

The bright white areas are thought to be carbon monoxide frost.

The images appear blurry because even Hubble can only resolve surface variations on the distant world that are a few hundred kilometres across, so the detailed geography of Pluto's surface remains unknown.

The Hubble images will be the sharpest view of the dwarf planet until NASA's New Horizons probe flies by in 2015.

Pluto was considered a planet after its discovery in 1930, but was demoted to dwarf planet status in 2006 when the International Astronomical Union defined new guidelines on what is considered a planet.