Cryovolcanic Constructs on Pluto

Pluto's surface has experienced considerable endogenic and exogenic resurfacing [1]. The terrains on Pluto represent a variety of ages, from seemingly ancient to surprisingly young. Some of the very young terrains are the result of the volatile ices on Pluto's surface (e.g., the convecting nitrogen-ice-rich plains of Sputnik Planitia). But Pluto also has several examples of more recent activity (terrains with few-to-no superimposed craters), that appear to be primarily made out of non-volatile water ice. The most prominent examples of potential cryovolcanism are two enormous topographic constructs with wide, deep central depressions [2]. The informally named Wright Mons stands 4 km high and the main mound spans 150 km. The informally named Piccard Mons is 7 km high and 225 km wide. The central depressions are dissimilar from a typical terrestrial shield volcano in that they are much wider (e.g., the Wright Mons central depression is 40-45 km wide, taking up 1/3rd of the total feature width) and deeper (the floors extend down to or below the level of the surrounding terrain). The central depression of Wright does not exhibit wall terraces that are typical indicators of collapse in terrestrial volcanoes. Instead, the central depression walls and floor have a large-scale hummocky texture similar to that the exterior of Wright, with individual hummocks on average 8-10 km across. A few terrains around Wright may be older, more fractured or cratered, examples of the terrain on the flanks. Thus there is some evidence for multiple episodes of terrain emplacement, but distinct flow fronts are not obvious. Each potential example of cryovolcanism found in the outer solar system is unique, and Pluto's features expand the information we have to understand this enigmatic process. We will present image, topographic, and composition data for Wright and Piccard along with geologic mapping results. We will discuss potential formation mechanisms in light of available empirical and model constraints. [1] Moore, J.M. et al. (2016) Science 351, 1284-1293. doi:10.1126/science.aad7055 [2] Singer, K.N. et al. (2016) Planetary Mappers Meeting 1920, #7017, http://adsabs.harvard.edu/abs/2016LPICo1920.7017S.