IMPLICATIONS FOR THE GEOLOGICAL AND GEOGRAPHICAL SIMILARITIES OF ICY SATELLITES

Icy satellites of the outer solar system host a variety of terrain types, geologic features, and preservation of geological histories. Many of the mid-sized to large icy moons are thought to host subsurface oceans today, or have hosted oceans in the past. The presence or absence of oceans has implications for understanding the possibility of habitable environments, amplified tidal stresses, and motions of the outer icy outer layers of these moons. Here we compare the geology and geography of two similarly sized icy satellites: Enceladus (radius ~250 km), a moon of Saturn; and Miranda (radius ~240 km), a moon of Uranus. Both moons possess regions that appear young and tectonically complex next to terrains that appear old and heavily cratered. The boundaries between the younger and older terrains are commonly sharp. Both moons have tectonically disrupted south polar regions and other disrupted terrains on the leading and trailing hemispheres. Additionally, the trends and wavelengths of the tectonics on the leading hemispheres of both moons are strikingly similar. The geographical similarities suggest both moons may have experienced a reorientation, possibly related to the tectonic deformation events. Reorientations of the icy shells are more likely if these moons possessed global subsurface liquid water layers that allow the exterior and interior to be decoupled. The similar trends and wavelengths of the tectonically disrupted terrains may point to similar ice shell thicknesses and viscosities at the time of deformation. Questions remain about how these relatively small worlds could experience such intense tectonic deformation in some areas while leaving other regions with few disruptions. However, given the similarities, both moons may have experienced comparable tectonic driving mechanisms in their past.