Exploring the Sensitivity of Lunar Interior Structure from Geophysical
and Geochemical Constraints
Abstract
Abstract The key to evaluating the formation history and evolution of
the Moon lies in understanding the current state of its interior. We
used a multidisciplinary approach to explore the current day lunar
structure and composition with the aim of identifying signatures of
formation and early evolution. We constructed a large number of 1D lunar
interior models to explore a wide range of potential structures and
identified those models that match the present day mass, moment of
inertia, and bulk silicate composition of the Moon. In an advance on
previous studies, we explicitly calculate the physical and elastic
properties of the varying mineral assemblages in the lunar interior
using multicomponent equations of state. We considered models with
either a compositionally homogeneous mantle or a stratified mantle that
preserved remnants of magma ocean crystallization, and tested thermal
profiles that span the range of proposed selenotherms. For the models
that reproduced the observed mass and moment of inertia, we found a
narrow range of possible metallic (iron) core radii (269-387 km)
consistent with previous determinations. We explored the possibility of
an ilmenite bearing layer both below the crust and at the core-mantle
boundary as a potential tracer of magma ocean solidification and
overturn. We observed a trade-off between the mass of the upper and
lower ilmenite-bearing layers and structures that have undergone mantle
overturn are both consistent with present observations. Plain Language
Summary In order to understand how the Moon formed, along with the
following history including the processes that change and shape it, the
current state of the lunar interior offers a lot of valuable information
or clues. We used several different computer simulation tools from
different disciplines to calculate the Moon’s interior structure. We
then compared our calculations with observations of the Moon’s mass and
moment of inertia (a measure of how its weight is distributed through
the interior) and the average composition and chemistry of the Moon. We
considered a Moon that is well mixed and one that has preserved layers
from its early history and tried different temperature structures. We
find that the Moon has to have a small dense iron core and that it may
have a hot soft layer just above the core that can dampen moonquakes.