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Enceladus and Europa, two icy satellites in our solar system, share similar surface temperatures and mean ice thickness. Despite that, their ice shell geometries are likely to be very different. Gravity and shape measurements taken on Enceladus favor a strongly poleward thinning ice shell, whereas Europa’s ice shell seems to be much flatter, supported by its limb profile.
This work proposes a mechanism to explain such a difference, which may be generalized to make predictions for other icy satellites. The key behind is the ocean dynamics. Driven by the temperature and salinity gradients underneath a thickness-varying ice shell, overturning circulations and baroclinic eddies will form, redistributing heat and tracers over the globe. The ocean heat transport (OHT) will, in turn, flatten the ice shell through the ice-pump mechanism. The efficiency of the OHT, however, varies with the satellite’s size and rotation period. In this work, we derive scaling laws that govern the OHT amplitude, verify the scalings using numerical simulations, and use them to predict the equilibrium ice thickness variations for icy moons with various sizes and rotation periods. Because of Europa’s strong gravity and slow rotation, its ice thickness variation is predicted to be less than 2km, in contrast to a 12+km ice thickness variation predicted for Enceladus. Given the OHT scaling laws, we demonstrate the possible ice evolution pathways for Enceladus and Europa using an ice evolution model with parameterized OHT.
Delivery and loss of volatile elements and compounds (such as water, carbon, nitrogen and the noble gases) during Earth’s accretion set the stage for the rest of our planet's history. Volatiles were gained through delivery by accreting solids and magma ocean ingassing during the lifetime of the solar nebula, and lost from the Earth system by impact-driven magma ocean outgassing and loss to space. Delivery and loss were each recorded by different noble gas isotope systems, making these sensitive tracers of important early-Earth processes. Here Dr. Parai presents new insights into the mix of materials that delivered volatiles to the growing Earth, and the signatures of early differentiation that persist in the mantle today.
Mineral–microbe interactions play important roles in environmental change, biogeochemical cycling of elements and formation of ore deposits across various spatial and temporal scales over Earth history. Minerals provide both beneficial (physical and chemical protection, nutrients, and energy) and detrimental (toxic substances and oxidative pressure) effects to microbes. Microbes impact dissolution, transformation and precipitation of minerals through their activity. The co-evolution of mineral-microbe interactions propels the evolution of Earth’s geosphere and biosphere. At the Earth’s beginning, there were only a few dozen high temperature minerals (geological species). After the Great Oxidation Event (GOE), the mineral species increased to >4000. The origination of eukaryotic organisms led to the formation of some organo-minerals, with the total number of mineral species reaching a modern level of >5000. Likewise, microorganisms experienced a long evolutionary history, from obligate anaerobe on early Earth to various aerobes in modern environments. Throughout Earth history, mineral-microbe interactions have widely occurred at the microscopic scale but the effect is often seen at the global scale.
This talk will focus on the geological, climatic, environmental, and biological perspectives to examine mineral–microbe co-evolution, with the aim of improving our understanding of mechanisms and driving forces behind their contributions to the origin of life and significant geological events such as GOE and the formation of ore deposits.