The Pluto-facing hemisphere of Charon displays two major terrain types: the heavily tectonized Oz Terra that stretches from the mid-latitudes to over the north pole and the relatively smooth equatorial low plains of Vulcan Planitia. While this encounter hemisphere of Charon was the best observed during the New Horizons flyby, we can use our knowledge of features and processes there to inform our interpretation of the remaining lower-resolution images of the far side of Charon.
The Pluto-Charon system revolves in 6.38 days, and we have images that differ in resolution by a factor of 40 from the beginning of the last-rotation-before-encounter to closest approach. The ground scale of whole-disk images ranges from 40 km/pixel up to 0.88 km/pixel.
These images allow us to examine the terrain around Butler Mons and its nearby scarps. It was speculated that the scarps to the east of Butler might be a southern boundary to Vulcan Planitia, but analysis of these images indicates that they are not, and Vulcan extends as far south as New Horizons could observe.
Only the largest craters can be identified and they are 20 to 145 km in diameter. In the better-resolved, westernmost area some morphological indicators can help, but elsewhere craters can only be inferred from the existance of bright albedo rings. There is also one example with a possible bright ray, but that identification is uncertain.
Large scarps, as seen on the encounter hemisphere can be identified in the far side images, and a similar population is found which implies that the heavily tectonized terrain seen in Oz Terra extends all the way around Charon, as expected. Furthermore, these large scarps also appear at latitudes below the northernmost boundary of Vulcan Planitia, indicating that Vulcan, while extensive, does not encircle Charon.
Finally, we have tentatively identified a large area (approximately 400 km across) on the far side devoid of large scarps that may be another large smooth plains unit, separate from Vulcan Planitia, but may be similar in character.