Name: Large H2O solubility in dense silica and its implications for the interiors of water-rich planets
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Large H2O solubility in dense silica and its implications for the interiors of water-rich planets

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Edited by Neta A. Bahcall, Princeton University, Princeton, NJ, and approved March 9, 2020 (received for review October 8, 2019)This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.Astrophysical observations have shown that Neptune-like planets are common in our galaxy (sub-Neptunes). Some of these exoplanets are believed to be covered with a thick O layer (100 to 1,000 km in thickness) above the rocky mantle (“waterworlds”). In order to understand the inner workings of the water-rich planets, it is important to understand the state of matter incorporating ice- and rock-forming elements at high-pressure and high-temperature conditions. Here, we report experimental evidence that silica and water have significant mutual solubility at high pressure and high temperature, forming new phases containing substantial amounts of both H and Si in oxide forms. Therefore, the boundary between rock and ice layers may be “fuzzy” at the deep interiors of water-rich planets.Sub-Neptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter in O-rich setting at high pressures and temperatures () places important limitations on our understanding of this planet type. We have conducted experiments for reactions between and O as archetypal materials for rock and ice, respectively, at high . We found anomalously expanded volumes of dense silica (up to 4%) recovered from hydrothermal synthesis above ∼24 GPa where the -type (Ct) structure appears at lower pressures than in the anhydrous system. Infrared spectroscopy identified strong OH modes from the dense silica samples. Both previous experiments and our density functional theory calculations support up to 0.48 hydrogen atoms per formula unit of (). At pressures above 60 GPa, O further changes the structural behavior of silica, stabilizing a niccolite-type structure, which is unquenchable. From unit-cell volume and phase equilibrium considerations, we infer that the niccolite-type phase may contain H with an amount at least comparable with or higher than that of the Ct phase. Our results suggest that the phases containing both hydrogen and lithophile elements could be the dominant materials in the interiors of water-rich planets. Even for fully layered cases, the large mutual solubility could make the boundary between rock and ice layers fuzzy. Therefore, the physical properties of the new phases that we report here would be important for understanding dynamics, geochemical cycle, and dynamo generation in water-rich planets.Published under the .You may purchase access to this article. This will require you to if you don't already have one.Subscribers, for more details, please visit our .Please click to log into the PNAS submission website.Large H2O solubility in dense silica and its implications for the interiors of water-rich planetsLarge H2O solubility in dense silica and its implications for the interiors of water-rich planetsEvidence of magnetism in Earth’s oldest minerals suggests a strong magnetic field around 4 billion years ago.Image credit: Julie Mansy (photographer), Rory D. Cottrell (University of Rochester, Rochester, NY), and John A. Tarduno (University of Rochester, Rochester, NY).Social tipping interventions could enable decarbonization and help mitigate climate change, according to a study.Image credit: Pixabay/paulbr75.Albatrosses could help monitor and detect undeclared fishing vessels at sea, according to a study.Image credit: Henri Weimerskirch.QnAs with biochemical engineer Jens NielsenImage courtesy of Jens Nielsen.Adam Millard-Ball and Chris Barrington-Leigh explain trends in urban street network design.

Edited by Neta A. Bahcall, Princeton University, Princeton, NJ, and approved March 9, 2020 (received for review October 8, 2019)This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.Astrophysical observations have shown that Neptune-like planets are common in our galaxy (sub-Neptunes). Some of these exoplanets are believed to be covered with a thick O layer (100 to 1,000 km in thickness) above the rocky mantle (“waterworlds”). In order to understand the inner...

Large H2O solubility in dense silica and its implications for the interiors of water-rich planets

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