Fluid Migration During Ice/Rock Planetesimal Differentiation

• Main Author: Raney, Robert 1987-
• Other Authors: Sparks, David
• Format: Others
• Published: 2013
• Subjects: Differentiation; Compaction; Planetesimal
• Online Access: http://hdl.handle.net/1969.1/148317

Much speculation on extraterrestrial life has focused on finding environments where water is present. Heating of smaller icy bodies may create and sustain a possible liquid layer below the surface. If liquid water was sustained for geologically significant times (> 108 years) within the ubiquitous small bodies in the outer solar system, the opportunities for development of simple life are much greater. The lifetime of the liquid water layer will depend on several factors, including the rate of rock/water reaction, which will depend on the rate at which water can be segregated from a melting ice/rock core. For the liquid water phase to migrate toward the surface, the denser rock phase must compact. The primary question that this thesis will answer is how fast melt water can segregate from the core of an ice-rich planetesimal. To answer this question we treat the core as two phase flow problem: a compacting viscous “solid” (ice/rock mixture) and a segregating liquid (melt water). The model developed here is based on the approach derived to study a different partially molten solid: in the viscously deforming partially molten upper mantle. We model a planetesimal core that initially a uniform equal mixture of solid ice and rock. We assume chondritic levels of radiogenic heating as the only heat source, and numerically solve for the evolution of solid and melt velocities and the distribution of melt fraction (“porosity”) during the first few million years after accretion. From a suite of numerical models, we have determined that the meltwater is segregated out of the core as fast as it is created, except in the case of very fast melting times (0.75 My vs. 0.62 My), and small ore radius (~25 to 150 km, depending on the viscosity of the ice/rock mixture in the solid core). In these latter cases, segregation is slower than migration and a high water fraction develops in the core. Heat released by water-rock reactions (not included in this model) will tend to drive up melting rates in all cases, which may favor this latter endmember.