  NASA's New Horizons spacecraft has revealed the complex geology of Pluto and
Charon. Pluto's encounter hemisphere shows ongoing surface geological activity
centered on a vast basin containing a thick layer of volatile ices that appears
to be involved in convection and advection, with a crater retention age no
greater than $\approx$10 Ma. Surrounding terrains show active glacial flow,
apparent transport and rotation of large buoyant water-ice crustal blocks, and
pitting, likely by sublimation erosion and/or collapse. More enigmatic features
include tall mounds with central depressions that are conceivably cryovolcanic,
and ridges with complex bladed textures. Pluto also has ancient cratered
terrains up to ~4 Ga old that are extensionally fractured and extensively
mantled and perhaps eroded by glacial or other processes. Charon does not
appear to be currently active, but experienced major extensional tectonism and
resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater
populations on Pluto and Charon are not consistent with the steepest proposed
impactor size-frequency distributions proposed for the Kuiper belt.
