Pluto has been revealed to be more dynamic than previously thought. New images, taken with Hubble’s revived Advanced Camera for Survey’s High Resolution Camera, reveal changing surface features where the changes are likely caused by ice sublimiating at the poles of the dwarf planet and then redistributing to other parts of the surface. The color is believed to be caused by ultraviolet light from the Sun breaking up methane on the surface. From the press release:
The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. These are driven by seasonal changes that are as much propelled by the planet’s 248-year elliptical orbit as its axial tilt, unlike Earth where the tilt alone drives seasons. The seasons are very asymmetric because of Pluto’s elliptical orbit. Spring transitions to polar summer quickly in the northern hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.
In addition to providing new insight into Pluto, the images are also going to help define observation plans for the New Horizons mission, due to arrive at Pluto in 2015. There is a great writeup about the press release over at Wired Science. The camera that captured the new images was previously out of commission but was repaired during a unprecedented spacewalk during Hubble’s Servicing Mission 4 where the individual circuit boards were removed during a spacewalk and replacement electronics were installed.