The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg.m(-3) for the hydrated silicates, and 300 to 500 kg.m(-3) for the dry silicates, due to the high iron bulk concentration in CI. The stability of Na-phlogopite in the silicate fraction up to 1300 K favors the trapping of most K-40 in the rocky/carbonaceous cores with important consequences for modeling of the thermal evolution of icy satellites. We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of similar to 30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system. (C) 2019 Elsevier B.V. All rights reserved.

Hydrated minerals are tracers of early solar system history and have been proposed as a possible focus for economic activity in space. Near-Earth objects (NEOs) are important to both of these, especially the most accessible members of that community. Because there are very few identified hydrated NEOs, we use the Ch spectral class of asteroids as a proxy for hydrated asteroids and use published work about NEO delivery, main-belt taxonomic distributions, NEO taxonomic distributions, and observed orbital distributions to estimate the number of hydrated asteroids with different threshold sizes and at different levels of accessibility. We expect 5327 Ch asteroids to be present in the known population of NEOs >1-km diameter, and using two different approaches to estimate accessibility we expect 179 of them to be more accessible on a round trip than the surface of the Moon. If there is no need to define a minimum size, we expect 700350 hydrated objects that meet that accessibility criterion. While there are few unknown NEOs larger than 1km, the population of smaller NEOs yet to be discovered could also be expected to contain proportionally many hydrated objects. Finally, we estimate that hydrated NEOs are unlikely to bring enough water to account for the ice found at the lunar poles, though it is possible that asteroid-delivered hydrated minerals could be found near their impact sites across the lunar surface. Plain Language Summary We know that some asteroids formed with water ice, and that early in solar system history that ice melted and reacted with rock to create hydrated minerals, which have water as part of their structure. Asteroidal hydrated minerals are particularly interesting because they often are found along with organic materials, and it is thought that asteroids may have been important for bringing water and organic materials to the early Earth via impacts. Hydrated minerals are also of interest to asteroid mining companies, which hope to make their extraction and processing as the basis for their business. For these reasons, we are interested in understanding how common hydrated asteroids are in the population of objects with orbits like the Earth's. There are a few different ways we can make the calculation, but all of the estimates suggest that hydrated asteroids are more common than we would think from the pieces that fall to Earth, and that dozens of them are larger than 1 km in diameter and take less fuel for a round-trip spacecraft than to the surface of the Moon.

Volatile lithophile elements are depleted in the different planetary materials to various degrees, but the origin of these depletions is still debated. Stable isotopes of moderately volatile elements such as Zn can be used to understand the origin of volatile element depletions. Samples with significant volatile element depletions, including the Moon and terrestrial tektites, display heavy Zn isotope compositions (i.e. enrichment of Zn-66 vs. Zn-64), consistent with kinetic Zn isotope fractionation during evaporation. However, Luck et al. (2005) found a negative correlation between delta Zn-66 and 1/[Zn] between CI, CM, CO, and CV chondrites, opposite to what would be expected if evaporation caused the Zn abundance variations among chondrite groups. We have analyzed the Zn isotope composition of multiple samples of the major carbonaceous chondrite classes: CI (1), CM (4), CV (2), CO (4), CB (2), CH (2), CK (4), and CK/CR (1). The bulk chondrites define a negative correlation in a plot of delta Zn-66 vs 1/[Zn], confirming earlier results that Zn abundance variations among carbonaceous chondrites cannot be explained by evaporation. Exceptions are CB and CH chondrites, which display Zn systematics consistent with a collisional formation mechanism that created enrichment in heavy Zn isotopes relative to the trend defined by CI-CK. We further report Zn isotope analyses of chondrite components, including chondrules from Allende (CV3) and Mokoia (CV3), as well as an aliquot of Allende matrix. All chondrules are enriched in light Zn isotopes (similar to 500 ppm on Zn-66/Zn-64) relative to the bulk, contrary to what would be expected if Zn were depleted during evaporation, on the other hand the matrix has a complementary heavy isotope composition. We report sequential leaching experiments in un-equilibrated ordinary chondrites, which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca. +0.65 per mil on Zn-66/Zn-64. We suggest isotopically heavy sulfides were removed from either chondrules or their precursors, thereby producing the light Zn isotope enrichments in chondrules. (C) 2017 The Author(s). Published by Elsevier B.V.