P088-06
Challenges on Mercury’s interior structure

Thursday, 17 December 2020: 04:20
Virtual
Gregor Steinbrügge, Stanford University, Department of Geophysics, Stanford, CA, United States, Mathieu Dumberry, University of Alberta, Edmonton, AB, Canada, Attilio Rivoldini, Royal Observatory of Belgium, Brussels, Belgium, Gerald Schubert, UCLA, Los Angeles, CA, United States, Hao Cao, Harvard, Boston, MA, United States, Dustin M Schroeder, Stanford University, Department of Geophysics, Department of Electrical Engineering, Stanford, CA, United States and Krista Marie Soderlund, University of Texas at Austin, Institute for Geophysics, Austin, TX, United States
Recorded Presentation
Abstract:
We calculated interior structure models based on recent measurements of Mercury’s obliquity and tides. Our models are consistent with the mean density, the moment of inertia (MoI), the ratio of the mantle to whole planet MoI (Cm/C) of Mercury. Further, we consider the tidal Love number k2 and account for iron snow formation. For Mercury’s core, we consider Fe-S as well as Fe-Si compositions. The equation of state for Fe-S and Fe-Si have been derived from recent laboratory measurements presented in [1]. We confirm that models that match a MoI=0.346, as deduced from an ensemble of obliquity measurements [2,3] and used in previous studies [4,5], are generally compatible with our present-day view of Mercury. In contrast, models that match a MoI=0.333, based on a recent obliquity [6] measurement pose a challenge to our current understanding of Mercury. Specifically, they feature a mantle density below 3100 kg/m3 for most models, lower than expected for typical planetary mantle minerals, and core radii between 1960 and 1990 km, inconsistent with magnetic induction measurements [7]. In addition, models that have a MoI=0.333 and agree with the tidal Love number k2 require low viscosities in the lower mantle that are difficult to reconcile with possible thermal histories of Mercury due to high temperatures at the core–mantle boundary (CMB). Hence, the structure of Mercury’s interior remains ambiguous and still leaves room for speculation. Possible new constraints could come from thermal evolution models, further laboratory measurements, especially for Fe-Si compositions under Mercury core conditions or a more precise measurement of the geodetic constraints as envisioned by BepiColombo mission [8] which is currently on its way to Mercury.

References: [1] Terasaki, H., et al. (2019) JGR: Planets 124, 2272– 2293; [2] Margot, J.-L., et al., (2007) Science 316, 710–714; [3] Stark, A., et al. (2015) GRL 42, 7881–7889 [4] Dumberry, M., & Rivoldini, A. (2015) Icarus 248, 254–268; [5] Steinbrügge, G., et al. (2018) JGR: Planets 123, 2760–2772; [6] Genova, A., et al. (2019) GRL 46, 3625–3633; [7] Wardinski, I., et al. (2019) JGR: Planets, 124, 2178-2197; [8] Benkhoff, J., et al. (2010). PSS, 58, 2–20;

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