Ref: CTALK-2022-0016

The Structure of the Martian Core Revealed by RISE

Rivoldini, Attilio ; Le Maistre, Sébastien ; Caldiero, Alfonso ; Yseboodt, Marie ; Dehant, Veronique ; Baland, Rose-Marie ; Van Hoolst, Tim ; Péters, Marie-Julie ; Beuthe, Mikael ; Marty, Jean-charles ; Folkner, William ; Buccino, Dustin ; Kahan, Daniel S ; Antonangeli, Daniele ; Panning, Mark P ; Banerdt, William Bruce

Talk presented at AGU Fall Meeting 2021, New Orleans, online on 2021-12-16

Abstract: After more than 2 years of monitoring the rotation of Mars with the RISE instrument on InSight, the effect of the planet’s core on the nutation (small periodic variations of the orientation of Mars spin axis in space) have been measured. From the acquired Doppler data we have confirmed the liquid state of the core, constrained its moment of inertia, and estimated, for the first time for a planetary body other than the Earth, the period of the Free Core Nutation (FCN) rotational normal mode. The FCN occurs because the instantaneous rotation axes of the mantle and the elliptical liquid core are misaligned. The knowledge of the FCN period provides unique insights about the moment of inertia of the core, its dynamical flattening, and its ability to deform as well as information about the coupling between the mantle and core. Mars dynamical flattening deviates significantly from that of a uniformly rotating fluid body and likewise, deviations from that state can be expected for the core. The validity of core shape predictions from models that aim to explain the dynamical shape of Mars can thus be assessed by comparing them to nutation observations. Unlike the FCN period, nutation amplitudes are less sensitive to the dynamical shape of the core. When combined with interior structure modeling, nutation data allows to deduce the radius of the core and constrain its fraction of light elements. Our inferred core radius agrees with previous estimates based on geodesy data and seismic data obtained with the InSight seismometer. The large fraction of light elements required to match the core density implies that its liquidus is significantly lower than any plausible estimate of its present-day temperature, and as such, the presence of an inner core is highly unlikely, although the presence of remelting iron-rich snow in the core cannot be excluded. An inner core would also lead to an additional rotational normal mode that could potentially be measurable, but its signature has not been detected in the RISE data. The estimated period of the FCN is best matched if the shape of the core resembles that of a rotating fluid planet or if the effective long-term rotating figure of Mars behaves like a rotating fluid overlain by an elastic shell of substantial thickness, comparable to the lithosphere thickness deduced from studies based on seismic data.

Keyword(s): Mars, RISE, core, rotation

The record appears in these collections:
Conference Contributions & Seminars > Conference Talks > Contributed Talks
Royal Observatory of Belgium > Reference Systems & Planetology

 Record created 2022-01-20, last modified 2022-01-20

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