Detection of the Liquid Core Signature in Mars Nutations from InSight-RISE Data: Implications for Mars Interior Structure

Fundamental properties of the interior structure and atmosphere dynamics of Mars can be obtained by precisely measuring its rotation [1]. We report the results of almost four Earth years of monitoring the rotation of Mars with the RISE instrument on InSight. Small periodic variations of the spin axis orientation, called nutations, can be extracted from the Doppler data with enough precision to identify the influence of the Martian fluid core. For the first time for a planetary body other than the Earth, we can measure the period of the Free Core Nutation (FCN), which is a rotational normal mode arising from the misalignment of the rotation axes of the core and mantle. In this way, we confirm the liquid state of the core and estimate its moment of inertia as well as its size and composition