Liquid water seems to play a crucial role in the evolution of dwarf planets. Despite their small sizes (radius of ca. 500 km), Ceres and KBOs such as Charon bear evidence for subsurface liquid water and aqueous chemistry products brought to the surface. How did water remain liquid? Is it still there? Thermal models of KBOs with time evolution, partial differentiation, and ammonia antifreeze have shown that they are capable of sustaining subsurface liquid water even to the present day, despite frigid surface temperatures. Subsurface liquid was predicted to persist on bodies as small as Charon until present. Models were also used to study the evolution of Ceres, showing that it too can maintain subsurface liquid because of a warmer surface. Since bodies with radii above only 500 km seem able to have liquid, these models are applicable to many dwarf planets. Geochemical processes have not been considered in thermal models, which assume that antifreezes like ammonia remain in the subsurface liquid for many Gyr, despite predictions of time-independent geochemical models that ammonia could form ammonium salts, less efficient antifreezes, or oxidize to N2. The modification of rock thermal properties upon hydration is another prime example of how geochemistry must be coupled to geophysics, to investigate dwarf planet evolution and liquid persistence. To address the geochemical deficiencies of thermal evolution models, we propose to: 1. Model the types of fluid flow on small bodies: (a) convection-driven hydrothermal circulation through a permeable core, cracked from thermal contraction, and (b) analytical conditions to initiate cryovolcanism. 2. Use available geochemical codes to model abundances of species in the subsurface fluid, including temperature and chemistry as fluid rises to the surface, and minerals produced by water-rock interaction, to produce a geochemistry subroutine to be used in thermal evolution codes. 3. Predict internal structure and chemistry of dwarf planets, and composition of material carried to their surface, to enhance science return from New Horizons and Dawn when they reach Ceres and Charon in 2015. Our modeling effort will predict the abundance of salts and hydrated minerals on the surfaces of dwarf planets for different outcomes of evolution scenarios. We will focus on making predictions allowing observations of Charon and Ceres by New Horizons and Dawn to discriminate between scenarios for the origin and evolution for these bodies. This basic research addresses two overarching questions of the 2010 Planetary Decadal Survey, and supports two SMDs Planetary Science missions. It will be the bulk of M. Neveus Ph.D. thesis, with help from S. Desch (ASU, adviser), E. Shock (ASU, secondary adviser), and J. Castillo-Rogez (NASA JPL, collaborator). It will be carried in concert with work at JPL by J. Castillo-Rogez and S. Vance to study the interaction of geophysics and geochemistry in icy bodies.
|Effective start/end date||9/1/14 → 8/31/16|
- NASA: Goddard Space Flight Center: $59,590.00