Gravitational-wave Tomography of the Moon: Constraining Lunar Structure with Calibrated Gravitational Waves

Author(s)

Yan, Han, Harms, Jan

Abstract

The recent success of gravitational-wave (GW) astronomy together with renewed plans for lunar geophysical instrumentation has revived interest in using the Moon as a resonant detector for mid-frequency (mHz-Hz) GWs. In realistic observational scenarios, the GW strain amplitude is expected to be constrained independently by networks of GW detectors, which motivates an inverse, \emph{tomographic} question: to what extent can measurements of the Moon's seismic response to known GWs be used to infer its internal structure? In this work, we develop a first-principles, perturbative framework that maps spherically symmetric perturbations of the elastic and density structure to measurable changes in observables, especially GW-driven modal amplitudes of the Moon. The formalism combines (i) a normal-mode representation of the elastic response, (ii) first-order perturbation theory for eigenvalues and eigenfunctions, and (iii) a linearized observation model that links frequency and amplitude observables to model parameters (bulk and shear moduli, density, and interface locations) and their perturbations. We show that the estimation errors of the Moon's elastic parameters can be reduced by about an order of magnitude with observations of calibrated GWs.

Figures

MINEOS verifications for amplitude perturbation, $\delta v_s / v_s = 0.2\%$ in the inner core. Only modes within the linear range (25\% tolerance of deviation) are included.
Caption MINEOS verifications for amplitude perturbation, $\delta v_s / v_s = 0.2\%$ in the inner core. Only modes within the linear range (25\% tolerance of deviation) are included.
MINEOS verifications for amplitude perturbation, $\delta v_s / v_s = 0.2\%$ in the inner core. Only modes within the linear range (25\% tolerance of deviation) are included.
Caption MINEOS verifications for amplitude perturbation, $\delta v_s / v_s = 0.2\%$ in the inner core. Only modes within the linear range (25\% tolerance of deviation) are included.
Relative errors for $\rho,\kappa,\mu$ with different combinations of observables. All modes with $n \le 150$ are considered as observables, while the perturbation summations are done for modes $\le 200$.
Caption Relative errors for $\rho,\kappa,\mu$ with different combinations of observables. All modes with $n \le 150$ are considered as observables, while the perturbation summations are done for modes $\le 200$.
MINEOS examination for linearity range of $A(\delta v_s ) /A(\delta v_{s,base} )$ in the inner core.
Caption MINEOS examination for linearity range of $A(\delta v_s ) /A(\delta v_{s,base} )$ in the inner core.
MINEOS examination for linearity range of $A(\delta v_s ) /A(\delta v_{s,base} )$ in the inner core.
Caption MINEOS examination for linearity range of $A(\delta v_s ) /A(\delta v_{s,base} )$ in the inner core.
MINEOS examination for linearity range of $A(\delta v_p ) /A(\delta v_{p,base} )$ in the outer core.
Caption MINEOS examination for linearity range of $A(\delta v_p ) /A(\delta v_{p,base} )$ in the outer core.
MINEOS examination for linearity range of $A(\delta v_p ) /A(\delta v_{p,base} )$ in the outer core.
Caption MINEOS examination for linearity range of $A(\delta v_p ) /A(\delta v_{p,base} )$ in the outer core.
MINEOS examination for linearity range of $A(\delta d_i ) /A(\delta d_{i,base} )$ at the boundary between inner core and outer core.
Caption MINEOS examination for linearity range of $A(\delta d_i ) /A(\delta d_{i,base} )$ at the boundary between inner core and outer core.
MINEOS examination for linearity range of $A(\delta d_i ) /A(\delta d_{i,base} )$ at the boundary between inner core and outer core.
Caption MINEOS examination for linearity range of $A(\delta d_i ) /A(\delta d_{i,base} )$ at the boundary between inner core and outer core.
MINEOS verifications for amplitude perturbation, $\delta v_p / v_p = 0.2\%$ in the outer core. Only modes within the linear range are included.
Caption MINEOS verifications for amplitude perturbation, $\delta v_p / v_p = 0.2\%$ in the outer core. Only modes within the linear range are included.
MINEOS verifications for amplitude perturbation, $\delta v_p / v_p = 0.2\%$ in the outer core. Only modes within the linear range are included.
Caption MINEOS verifications for amplitude perturbation, $\delta v_p / v_p = 0.2\%$ in the outer core. Only modes within the linear range are included.
MINEOS verifications for amplitude perturbation, $\delta d_i / d_i = 0.2\%$ at IC-OC boundary. Only modes within the linear range are included.
Caption MINEOS verifications for amplitude perturbation, $\delta d_i / d_i = 0.2\%$ at IC-OC boundary. Only modes within the linear range are included.
MINEOS verifications for amplitude perturbation, $\delta d_i / d_i = 0.2\%$ at IC-OC boundary. Only modes within the linear range are included.
Caption MINEOS verifications for amplitude perturbation, $\delta d_i / d_i = 0.2\%$ at IC-OC boundary. Only modes within the linear range are included.
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