GLACIATION AND THRUST TECTONICS ON CHARON WITH IMPLICATIONS FOR THE KUIPER BELT EVOLUTION

Systematic geomorphological mapping and detailed landform analysis using the highest resolution images obtained by the New Horizons spacecraft reveal the presence of a range of differentiable terrains on Charon, the largest moon of Pluto, that were not examined in detail by the early studies. The most important findings of our work include (1) truncation and omission of large craters (diameters > 30-40 km) and their crater rim ridges along the eastern edges of several north-trending, eastward-convex, arcuate ranges in Oz Terra of the northern encountered hemisphere, (2) lobate ridges, lobate knob trains, and lobate aprons resembling glacial moraine landforms on Earth, (3) dendritic channel systems containing hanging valleys, and (4) locally striated surfaces defined by parallel ridges, knob trains, and grooves that are >40-50 km in length. The above observations and the topographic dichotomy of Charon’s encountered hemisphere can be explained by a landscape-evolution model that involves (i) a giant impact that created the Vulcan Planitia basin and the extensional fault zone along its northern rim, (ii) a transient atmosphere capable of driving N₂-ice glacial erosion of the water-ice bedrock and transporting water-ice debris to sedimentary basins, (iii) regional glacial erosion and transport of earlier emplaced impact ejecta deposits from the highlands of Oz Terra into the lowland basin of Vulcan Planitia, (iv) syn-glaciation north-trending thrusting interpreted to have been induced by Charon’s despinning, and (v) the development of a water-ice debris cover layer over subsurface N₂ ice below Vulcan Planitia during global deglaciation. The infilling of the Vulcan Planitia could have been accompanied by cryovolcanism. The extensive modification of impact craters means that the crater size-frequency distributions from Charon should serve only as a lower bound when used to test the formation mechanism of Kuiper belt objects.