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PLANETARY INTERIORS

Stardust in the deep interior of low-mass planets

Nature Astronomy volume 5, pages 744–745 (2021)Cite this article

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The behaviour of minerals under high pressure affects the bulk properties of exoplanets and planets with rocky components, possibly influencing their observable radii. Obtaining a wide range of experimental data is key to understanding observations and informing planetary interior models.

Low-mass planets are primarily made of heavy elements originating from fading stars. Under compression, these elements favour molecular states such as the mineral MgO and the ice H2O. Do these constituents organize themselves under the pressure of planetary deep interiors into the form of layers or does the disordering influence of high temperature take over? Writing in Nature Astronomy, Taehyun Kim et al.1 answer this question by using the static diamond anvil cell technique to compress rocks and water to planet-interior conditions of 20–60 GPa (200,000–600,000 times the air pressure). They investigate whether, when water is heated to ~1,400–1,800 K where it becomes a dense fluid, water and rocks would be miscible, as liquid water and salt are, or whether they prefer to phase separate, as liquid water and oil do. Kim et al. find that MgO, a typical component of the Earth’s rocky lower mantle, is soluble in fluid H2O at ~30 GPa and ~1,800 K, whereas its solubility decreases with increasing pressure.

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Fig. 1: Illustration of water–rock miscibility in low-mass planets.

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Authors and Affiliations

  1. Department of Extrasolar Planets and Atmospheres, DLR-Institute of Planetary Research, German Aerospace Center, Berlin, Germany

    Nadine Nettelmann

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  1. Nadine Nettelmann
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Correspondence to Nadine Nettelmann.

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Nettelmann, N. Stardust in the deep interior of low-mass planets. Nat Astron 5, 744–745 (2021). https://doi.org/10.1038/s41550-021-01421-0

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