Hubble reveals Pluto as “a dynamic world that undergoes dramatic atmospheric changes”

Something else for the Ingenious Mr Hooke to smile about. In preparation for an encounter with Nasa’s New Horizons mission, led by honker-in-chief Alan Stern, the Hubble Space Telescope had been looking closely again at the dwarf planet Pluto. And, as reported by the BBC, by comparing the newer images (taken in 2002-2003) with earlier Hubble images taken in 1994 [added link] they’ve seen evidence that, “The icy dwarf planet Pluto undergoes dramatic seasonal changes” in its 248-year-long cycle. Much more information at the Hubble Newscenter.

Hubble’s view isn’t sharp enough to see craters or mountains, if they exist on the surface, but Hubble reveals a complex-looking and variegated world with white, dark-orange, and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto’s surface, leaving behind a dark, molasses-colored, carbon-rich residue. Astronomers were very surprised to see that Pluto’s brightness has changed — the northern pole is brighter and the southern hemisphere is darker and redder. Summer is approaching Pluto’s north pole, and this may cause surface ices to melt and refreeze in the colder shadowed portion of the planet. The Hubble pictures underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes.

Below the fold astronomers explain the significance of the revealed changes. In the meantime, as spotted at WiredScience, here’s an animation of the latest Hubble images of Pluto. Video Credit: NASA, ESA, and M. Buie (Southwest Research Institute).
Adds For a rough comparison here is the Nasa/Esa animation of the Hubble images taken in 1994. These images were taken in blue light when Pluto was at a distance of 3 billion miles from Earth.

Astronomers explain the significance of new Hubble images revealing changes on the surface of Pluto. Video Credit: NASA, ESA, and M. Estacion (STScI).

From the text of the NASA press release

New Horizons will pass by Pluto so quickly that only one hemisphere will be photographed in detail. Particularly noticeable in the Hubble images is a bright spot that has been independently noted to be unusually rich in carbon monoxide frost. It is a prime target for New Horizons. “Everybody is puzzled by this feature,” Buie said. New Horizons will get an excellent look at the boundary between this bright feature and a nearby region covered in pitch-black surface material.

“The Hubble images also will help New Horizons scientists better calculate the exposure time for each Pluto snapshot which is important for taking the most detailed pictures possible,” Buie said. With no chance for re-exposures, accurate models for the surface of Pluto are essential for properly exposed images.

The Hubble images surface variations a few hundred miles across that are too coarse for understanding surface geology. But in terms of surface color and brightness, Hubble reveals a complex-looking world with white, dark-orange and charcoal-black terrain. The overall color is believed to be a result of ultraviolet radiation from the distant sun breaking up methane present on Pluto’s surface, leaving behind a dark and red-carbon-rich residue.