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Updated: Jul 13, 2026

Simulation of the Planetary Interior Differentiation Processes in the Laboratory
Published on: November 15, 2013
Large longitude libration of Mercury reveals a molten core
J L Margot1, S J Peale, R F Jurgens
1Department of Astronomy, Cornell University, 304 Space Sciences Building, Ithaca, NY 14853, USA. jlm@astro.cornell.edu
Abstract:
Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 +/- 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 +/- 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is decoupled from a core that is at least partially molten.
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