Evolution and Differentiation of Large Icy Moons
Abstract: Purpose: In preparation of several future missions with the objective to research the large icy moons of the Solar System, it is necessary to have a cohesive understanding of the conditions that might lead to the formation of liquid oceans in these moons. The purpose of this work is to create a numerical model for simulating the temperature evolution of the cores of large icy moons. Method: Assuming 1-D spherical geometry, this work constructs a numerical model determining the energy and consequent temperature evolution in the rocky cores of large icy moons under the influence of radiogenic heating from 40K, 235U, 238U and 232Th. Both conductive and convective heat transfer methods were considered with different fractions of potassium present to account for the potential leaching of this element into the water layers above. The endothermic process of dehydrating clay minerals was also implemented in this model. Results: Using the code the cores of Titan, Europa, Rhea and Mimas were simulated. It was determined that both core radius and remaining potassium fraction after leaching have significant effects on temperature evolution, with the highest possible temperatures reached in Titan with 100% of the potassium remaining at 3100 kelvins. However, using the often quoted fraction of 30% of the remaining potassium in the rocky cores, the temperatures in the cores of Titan and Europa are significantly lower, though continuing to increase at present day. When considering longer timescales, the core of Titan can undergo melting and subsequent metal-silicate differentiation even at the fraction of primordial potassium set to 30% of its original value. Conclusions: Even with low amounts of potassium remaining in the rocky cores of Titan and Europa, the presence of an ocean on top of them remains very likely. Furthermore, radiogenic heating alone is sufficient to lead to full differentiation into a metallic core, a silicate outer core and an ice mantle, provided the potassium fraction in the core is sufficient.
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