Free Astronomy Magazine September-October 2015

11 PLANETOLOGY a few billion years), set against brighter areas which ap- pear almost cra- terless and that should, there- fore, have form- ed much more recently (per- haps a hun- dred million years ago). In several places can be observed craters par- tially destroy- ed, perhaps by erosion, and al- so craters that appear invaded by layers of ligh- ter-coloured materi- al, proving the fact that Pluto has until relatively recently been geologically ac- tive, or that maybe it still is. 14 July, the Ralph in- strument reveals a concentration of frozen carbon monoxide (green area) in Tom- baugh Regio. Below, Sputnik Planum’s territo- ries characterized by polygonal- shaped features, whose nature is yet to be deter- mined. [NASA/ Johns Hopkins University Ap- plied Physics Lab- oratory/South- west Research Institute]