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Blobrana


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RE: Ice giants
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  Ice giant planets have more water volume than believed

The idea of compressing water is foreign to our daily experience.
Nevertheless, an accurate estimate of water's shrinking volume under the huge gravitational pressures of  large planets is essential to astrophysicists trying to model the evolution of the universe. They need to assume how much space is taken up by water trapped under high density and pressure, deep inside a planet, to calculate how much is needed of other elements to flesh out the planet's astronomical image.
In a challenge to current astrophysical models, researchers at Sandia National Laboratories and the University of Rostock in Germany have found that current calibrations of planetary interiors overstate water's compressibility by as much as 30 percent. The work was reported in the paper "Probing the Interior of the Ice Giants" in the Feb. 27 Physical Review Letters.
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Blobrana


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Title: Probing the interiors of the ice giants: Shock compression of water to 700 GPa and 3.8 g/ccm
Authors: M. D. Knudson, M. P. Desjarlais, R. W. Lemke, T. R. Mattsson, M. French, N. Nettelmann, R. Redmer

Recently there has been tremendous increase in the number of identified extra-solar planetary systems. Our understanding of their formation is tied to exoplanet internal structure models, which rely upon equations of state of light elements and compounds like water. Here we present shock compression data for water with unprecedented accuracy that shows water equations of state commonly used in planetary modelling significantly overestimate the compressibility at conditions relevant to planetary interiors. Furthermore, we show its behaviour at these conditions, including reflectivity and isentropic response, is well described by a recent first-principles based equation of state. These findings advocate this water model be used as the standard for modelling Neptune, Uranus, and "hot Neptune" exoplanets, and should improve our understanding of these types of planets.

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