Computer Science – Sound
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmgp32a..04c&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #GP32A-04
Computer Science
Sound
1515 Geomagnetic Induction
Scientific paper
We present a general method to constrain planetary composition and thermal state from a stochastic inversion of long-period electromagnetic sounding data. As an example of our approach, we reexamine the problem of inverting lunar day-side transfer functions to constrain the internal structure of the Moon. We go beyond the conventional approach by inverting directly for chemical composition and thermal state, using the model system CaO-FeO-MgO-Al2O3-SiO2, rather than subsurface electrical conductivity structure, which is only an indirect means of estimating the former parameters. Using Gibbs free energy minimisation, we calculate the stable mineral phases, their modes and densities. The mineral modes are combined with laboratory electrical conductivity measurements to estimate the bulk lunar electrical conductivity structure from which transfer functions are calculated. To further constrain the radial density profile in the inversion we also consider lunar mass and moment of inertia. The joint inversion of electromagnetic sounding and gravity data for lunar composition and selenotherm as posited here is found to be feasible. Our results are not only in line with earlier investigations of the lunar electrical conductivity structure, but also with investigations of the elastic properties (seismic velocities) of the Moon. Our results indicate a bulk composition that is different from the Earth's upper mantle, in line with the giant impact hypothesis for the formation of the Moon. In order to improve future inferences about lunar composition and thermal state, more electrical conductivity measurements are needed especially for minerals appropriate to the Moon, such as pyrope and almandine.
Connolly James
Khan Ashfaq A.
Olsen Nils
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