Scientists concluded that the mineralogical composition of the mantle of Mars may be similar to the upper mantle of the Earth.

Planetary scientists working with the seismograph SEIS of the Martian automatic station InSight have published new results of the analysis of the data collected by the device. Scientists were able to estimate the thickness of the crust of Mars, determine the size of the planet’s core, and find out that the crust is many times richer in radioactive elements than the planet’s mantle.

InSight landed on Mars at the end of 2018 and is engaged in research into the internal structure and climate of the planet. The station is equipped with several scientific instruments, but the most important of them is the SEIS seismograph, which recorded the first marsquake in March 2019 and has since detected more than a thousand individual seismic events.

An analysis of how seismic waves propagate inside the planet previously allowed scientists to roughly understand where the boundaries of the layers of Mars lie and what the size of its core is.

1. In three new papers, planetary scientists from the international InSight team, working with data obtained by SEIS, published the results of studies of the internal structure of Mars. Amir Khan of the Institute of Geophysics in Zurich and his colleagues used direct (P and S) and reflected from the surface (PP, PPP, SS, and SSS) seismic waves generated during eight Marsquakes to study the structure of the planet to a depth of 800 kilometers.

2. Scientists have determined that the lithosphere of Mars runs to depths of 400-600 kilometers, which makes it thicker than in the case of the Earth.

3. Moreover, in comparison with the mantle, the crust of Mars is 13-20 times richer in radioactive elements, the decay of which greatly heats this layer. These estimates turned out to be higher than those obtained during the exploration of the surface of Mars by orbiters.

4. Brigitte Knapmeyer-Endrun of the Institute of Geology and Mineralogy at the University of Cologne and her colleagues used seismic events to estimate the thickness and layering of Mars’ crust at the station’s landing site. Scientists have concluded that there may be two models of the crust: thin and thick.

5. In the case of a thin model, the crust is 15 to 25 kilometers thick and can be divided into two layers. In the case of a thick crust, its thickness will be from 27 to 47 kilometers and three layers can be distinguished in it.

6. If we consider the entire planet as a whole, then within the framework of the thin model, the average crustal thickness is from 24 to 38 kilometers, and its maximum permissible density is 2850 kilograms per cubic meter.

7. In the case of the thick model, the average crust thickness is 39 to 72 kilometers, and its maximum permissible density is 3100 kilograms per cubic meter. For both models, the crustal density turned out to be significantly lower than one would expect based on the properties of the surface layer of Mars.

8. Finally, (Simon C. Stähler) of the Institute of Geophysics in Zurich and his colleagues used seismic waves to refine the boundary between Mars’ mantle and its liquid metal core.

9. It turned out that the radius of the core is 1830 ± 40 kilometers, and its average density is from 5.7 to 6.3 grams per cubic centimeter, which requires a significant amount of light elements dissolved in the iron-nickel core, in particular sulfur (10-15 percent of the total mass), oxygen (<5 percent of the total mass), and hydrogen and carbon (<1 percent of the total mass).

10. Scientists concluded that the mineralogical composition of the mantle of Mars may be similar to the upper mantle of the Earth, while the planet lacks a relatively dense and heat-insulating lower mantle. This is consistent with the model in which Mars possessed a global magnetic field generated by the dynamo effect 4.5-3.7 billion years ago, and then cooled relatively quickly, due to which only magnetized parts of the planet’s crust can now be observed.

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Sources:

• Khan, A., Ceylan, S., & Driel, M. van. (2021, July 23). Upper mantle structure of Mars from InSight seismic data. Science.
• Knapmeyer-Endrun, B., Panning, M. P., & Bissig, F. (2021, July 23). Thickness and structure of the martian crust from InSight seismic data. Science.
• NASA. (2021, July 22). NASA’s InSight Reveals the Deep Interior of Mars – NASA’s Mars Exploration Program.
• O’Callaghan, J. (2021, July 22). InSight Lander Makes Best-Yet Maps of Martian Depths. Scientific American.
• Stähler, S. C., Khan, A., & Banerdt, W. B. (2021, July 23). Seismic detection of the martian core. Science.