Local modeling

Character of the Martian crust constrained by InSight and gravity modeling

An example of a global crust thickness model for uniform crust density. Credit: Wieczorek et al., 2022.

NASA’s interior exploration using seismic surveys, geodesy and heat transport (InSight) provided the first direct measurement of the thickness of the Martian crust by monitoring seismic waves from earthquakes. The crusts of terrestrial planets retain information about how these bodies formed and were modified by subsequent events such as magmatism or impacts. According to the currently preferred model, the crust of the InSight landing site extends down to 39 ± 8 kilometers in depth.

Mark A. Wieczorek of the Université Côte d’Azur, with collaborators, combined local InSight stresses with global gravity and topography data to infer the global character of the crust. Generally, anomalies in the observed planetary gravity field are due to the relief on a planet’s surface (i.e. its topography), the crust-mantle interface, and the mantle- core. Assuming the internal density structure, the relief at the crust-mantle interface can be calculated (and therefore also the crustal thickness) to satisfy both the observed global gravity field and the local crustal thickness measured by InSight.

Considering several reasonable density profiles, Wieczorek and his collaborators find that the average thickness of Mars’ crust is between 30 and 72 kilometers, with a maximum allowable density of 2850 to 3100 kilograms per cubic meter. This density is lower than that of the basalt materials observed on the surface and consistent with more felsic materials, relatively enriched in silica and which could have been derived from basalts by magmatic fractionation. Based on this result, the researchers suggest that the Martian crust that formed during the planet’s initial differentiation was covered by later volcanism. The wide range of estimated average crustal thicknesses is partly due to the uncertainty of InSight’s measurement of crustal thickness. Placing additional seismometers — especially in the southern highlands — to measure local crustal thickness at multiple points on Mars would help limit the overall estimate. READ MORE

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