11:45 AM - 12:00 PM
[SCG48-05] The Miscibility of H2 and H2O Investigated by Externally Laser-Heated Diamond Anvil Cells
Keywords:ice giants, diamond anvil cell
The conventional “three-layer model” of ice giants assumes that the planets can be separated into three distinct components: the H2-rich envelope, the H2O-rich mantle, and the rocky/metallic core (e.g. Redmer et al., 2011 Icarus; Nettelmann et al., 2013 Planet. Space Sci.; Bethkenhagen et al., 2017 Astrophys. J.). However, the view that the interior of ice giants is divided by well-defined boundaries has been challenged in recent years. Because there are two possible locations for a boundary, a total of four separate models can be conceptualized, and there is a lack of strong evidence from observations to identify a likely model (e.g. Helled et al., 2020 Space Sci. Rev.; Guillot et al., 2022 arXiv:2205.04100). From a materials science perspective, the question of whether a distinct boundary exists or not can be understood as how miscible the phases in the planetary interior are. If we focus on the envelope-mantle boundary, previous studies on the H2-H2O system have not yet conclusively answered whether the critical curve, which marks the boundary between miscibility and immiscibility, is above the temperature profile inside the ice giants.
In order to examine the possibility of a compositional boundary between the envelope and mantle of ice giants, here we performed high-pressure and -temperature observations on the miscibility between H2 and H2O up to 8.3 GPa and 540 ℃, based on a recently developed externally-laser-heated diamond-anvil cell technique (Okuda et al., 2023 Rev. Sci. Instrum.) with in-situ XRD measurements for pressure determinations. Our data show that hydrogen and water become miscible at conditions well below the temperature conditions of the ice giants’ interiors, suggesting that the envelope and mantle should not have a well-defined boundary.
In order to examine the possibility of a compositional boundary between the envelope and mantle of ice giants, here we performed high-pressure and -temperature observations on the miscibility between H2 and H2O up to 8.3 GPa and 540 ℃, based on a recently developed externally-laser-heated diamond-anvil cell technique (Okuda et al., 2023 Rev. Sci. Instrum.) with in-situ XRD measurements for pressure determinations. Our data show that hydrogen and water become miscible at conditions well below the temperature conditions of the ice giants’ interiors, suggesting that the envelope and mantle should not have a well-defined boundary.