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A multi model investigation of the global interior structure of the Moon

  • Author(s): Fuqua, Heidi
  • Advisor(s): de Pater, Imke
  • Delory, Greg
  • et al.
Abstract

We consider four modeling efforts to determine the interior structure of the Moon. This includes a geophysical forward model capturing magnetic induction from conducting layers within a vacuum, a plasma induction model capturing the kinetic plasma environment within the wake cavity around a conducting Moon, a multidisciplinary modeling analysis including geochemical, geophysical, and geodynamical considerations, and forward calculate the seismic free oscillations of the Moon.

Electromagnetic Sounding constrains conducting layers of the lunar interior by observing variations in the Interplanetary Magnetic Field disturbing the Moon. We employ the time domain transfer function method locating transient events observed by two magnetometers near the Moon. We consider ARTEMIS and Apollo magnetometer data. We demonstrate our forward model passes benchmarking analyses and solves the magnetic induction response for any input signal as well as any conductivity profile. Plasma hybrid models use the upstream plasma conditions and IMF to capture the wake current systems formed around the Moon. The plasma kinetic equations are solved for ion particles with electrons as a charge-neutralizing fluid. These models accurately capture the large-scale lunar wake dynamics for a variety of solar wind conditions (ion density, temperature, solar wind velocity, and IMF orientation). This method and modeling results are applicable to any airless body with a conducting interior, interacting directly with the solar wind in the absence of a parent body magnetic field as well as any two-point magnetometer constellation.

For our third analysis, we take a multidisciplinary approach to constrain key parameters of the lunar structure. We use an ensemble of 1D lunar compositional models with chemically and mineralogically distinct layers, and forward calculate physical parameters. We employ a grid search and a differential evolution genetic search algorithm to extensively explore model space, where the thickness of individual compositional layers varies. We find that the proposed partially molten layer within the deep mantle may have been formed by the overturn of an ilmenite rich layer, formed after the crystallization of a magma ocean. Moreover, only a narrow range of core radii are consistent with the mass and moment of inertia constraints. For the models that fit the observed mass and moment of inertia, we compare the deviation in the chemistry to that published, and calculate 1D seismic velocity profiles, the majority of which compare well with those determined by inverting the Apollo seismic data.

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