Electrical and seismological structure of the martian mantle and the detectability of impact-generated anomalies

We derive synthetic electrical conductivity, seismic velocity, and density distributions from the results of martian mantle convection models affected by basin-forming meteorite impacts. The electrical conductivity features an intermediate minimum in the strongly depleted topmost mantle, sandwiched between higher conductivities in the lower crust and a smooth increase towards almost constant high values at depths greater than 400 km. The bulk sound speed increases mostly smoothly throughout the mantle, with only one marked change at the appearance of $\beta$-olivine near 1100 km depth. An assessment of the detectability of the subsurface traces of an impact suggests that its signature would be visible in both observables at least if efficient melt extraction from the shock-molten target occurs, but it will not always be particularly conspicuous even for large basins; observations with extensive spatial and temporal coverage would improve their detectability. Electromagnetic sounding may be a more promising method for investigating the properties of impact structures than seismology and, as far as the mantle is concerned, than gravity. It could also help constraining the water content of the mantle in general. By comparing electromagnetic sounding data of an impact structure with model predictions, it might also be possible to answer the open question of the efficiency of impact-generated melt extraction.

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