VOLATILE-LITHOSPHERE RECYCLING OF OUTER ICY SATELLITES AND TRANS-NEPTUNIAN OBJECTS INFERRED FROM THERMAL GRADIENT MODELING OF TRITON’S ICE SHELL

Triton is a differentiated and active Kuiper Belt object captured by Neptune in the early solar system with volatile ices N₂, CO, CH₄, and CO₂ blanketing its surface. Solid or liquid volatile compounds on the surface of a volcanically active planetary body suggest a magmatic-tectonic distillation process that concentrates the volatiles in surface reservoirs, similar to Earth’s hydro-tectonic cycle where water is transferred to the Earth’s oceans and atmosphere from its interior. I investigate such a self-sustaining process occurring on Triton by using previously estimated thermophysical properties of Triton’s water ice lithosphere to determine the thermal gradient from the frigid surface to the subsurface ocean. Calculated average thermal gradients for Triton’s ice shell are ~0.65 K/km and ~1.05 K/km, a conclusion that implies volatile ices should exceed melting temperatures as they are vertically displaced into Triton’s interior by burial from surface cryovolcanism. Melting begins at relatively shallow depths as the isolated volatiles are buried deeper within Triton’s ice shell, given that the volatiles melt at much lower temperatures than the surrounding water ice. These isolated volatile melts are less dense than the water ice and remain stationary before being assimilated by cryomagmas that ascend Triton’s ice shell via crack propagation. The contributions of volatiles assist the cryomagmas in erupting onto the surface and later becoming remobilized as the lithospheric recycling process repeats. Therefore, I speculate collaborating endogenic thermal systems and vertical cycling of Triton’s ice shell extracts volatile compounds from its interior to the surface reservoirs by asthenospheric melting and magmatic assimilation analogous to Earth’s hydro-tectonic cycle (a “cryo-tectonic” cycle). This self-sustaining cycling process may be a common geological phenomenon associated with outer icy satellites and trans-Neptunian objects during their evolution.