Credit: NASA, ESA and M. Buie (SwRI).
The color changes are considered to be the result of methane ice sublimating into the atmosphere as the northern spring progresses. Paul Gilster at Centauri Dreams noted this gives rise to a new mystery:
I thought the liveliest part of the teleconference on Pluto yesterday was Marc Buie’s response to what had appeared in his datasets. Buie (Southwest Research Institute) was looking at imagery collected by the Hubble Space Telescope from 2002 to 2003 and comparing it with the results of earlier ground-based observations, as well as with Hubble pictures taken in 1994. The dramatic reddening seems to have occurred between 2000 and 2002, even as the illuminated northern hemisphere continued to get brighter.
Asked about his reactions to the newer Hubble imagery, Buie was candid:
“The color change in such a short period had me scared, because it’s so hard to understand. I’ve been checking absolutely everything I can think of, wondering if I screwed this up somehow and got the wrong answer. If I did, I can’t find the mistake.”
Another key point: In the Hubble imagery, the color of Charon remains the same throughout, whereas the reddening of Pluto is pronounced.
Something weird is going on way out there. The enigmatic object, now considered to be a Kuiper belt object has some stories to tell. Rather than a frozen ball of ice, Pluto is turning out to be a dynamic world, with seasons, an atmosphere and a varied surface silently lurking in the dark.