Conversation:

A recent study shows that Pluto is much more reflective on one face than on the one 180 around.
http://www.nasa.gov/images/content/421593main_i1006ay.jpg
they believe the brightest area is frozen Carbon Monoxide.

It's even on the BBC news website: http://news.bbc.co.uk/1/hi/sci/tech/8498455.stm

Pluto, it seems, gets more interesting. We'll know a lot more after New Horizons' flyby in 2015.