When the Hubble pictures taken in 1994 of Pluto are compared to 2002-2003 photo’s there are some dramatic changes like brightening of the Northern pole and more reddish coloration. Based on the latest studies and findings it is estimated that Pluto has more visible surface changes than any other planet in the solar system.
Researchers say the brightening in the northern hemisphere could be the result of nitrogen ice vaporizing at the sunlit pole and then refreezing at the opposite pole which is not illuminated, but do not have a reasonable explanation for why the red coloration shift is occurring.
Pluto also has such violent seasons due to its unusual orbit which has it almost the closest it has been to the Sun in decades, and it will be the furthest from the sun in the year 2108. By contrast Earth and Mars have visible changes with polar caps melting in the summer and growing in the winter, but this is not nearly as extreme as the seasons on Pluto.
Extremely detailed images of Pluto will come in 2015 when the New Horizons spacecraft will flyby Pluto and snapshot some of the most detailed photos of Pluto’s surface to analyze composition and make up.