Recently, a team of scientists participating in the National Aeronautics and Space Administration (NASA) InSight mission completed an analysis of seismic data recorded on Mars after a meteorite impact in September 2021. Their findings dramatically change our view of the Red Planet's internal structure and evolution.
Based on these results and previous geophysical data, Attilio Rivoldini, a researcher at the Royal Observatory of Belgium, participated in a study published in the journal Nature and proposed a new model of the interior of Mars, with a heterogeneous mantle containing a molten silicate layer above the liquid metal core.
Preliminary results and hypotheses
The first results based on data provided by the InSight mission significantly improve our understanding of the interior structure of Mars. Assuming that the mantle composition is uniform and completely solid, the results show that the radius of the liquid metal core is about 1830±40 kilometers, the density is relatively low (6-6.2 g/cm3), and it is rich in light elements. The size of the metallic core was determined by detecting seismic waves reflected from the solid-liquid interface, which is considered the core-mantle boundary (CMB).
Reassessment after recent impact
Since then, however, analysis of new data generated by a powerful meteorite impact on September 18, 2021, has cast doubt on initial estimates of Mars' internal structure. An international team of researchers, led by Henri Samuel, a researcher at the Institute of Geophysics in Paris of the French National Center for Scientific Research (CNRS), and involving Attilio Rivoldini of the Royal Observatory of Belgium, studied the travel times of these waves and showed that a layer of molten silicate at the base of Mars' mantle and above its metallic core could explain the new data.
Based on this discovery, a new structural model was derived and published in the journal Nature on October 26. Not only is the structural model more consistent with all available geophysical data, it also better explains how Mars has evolved since its formation.
Explanation of earthquake anomalies
A molten layer at the base of the mantle explains the unusually slow propagation of seismic waves diffracted along the CMB in September 2021, a phenomenon that has not yet been explained. Furthermore, for several earlier seismic events, the arrival times of seismic waves coincide with reflections of seismic shear waves at the top of the molten layer (tens of kilometers above the metallic core) rather than at the CMB as previously assumed.
Impact on core size and composition
The presence of a molten layer at the base of the mantle means that Mars' metallic core is 150 to 170 kilometers smaller than previous estimates (i.e., a radius of 1650 ± 20 kilometers).
"This smaller core is also 5 to 8 percent denser (i.e. 6.5 g/cm³). The proportion of light elements in the core is lower than previously thought and is therefore more consistent with cosmochemical data derived from analysis of Martian meteorites and high-pressure experiments," explains Attilio-Rivodini.
Therefore, the study authors propose that Mars experienced an early magma ocean stage, which crystallized to form a stable layer at the bottom of the mantle, rich in iron and radioactive elements. The heat released by radioactive decay creates a basal layer of molten silicates above the Earth's core.
References Henri Samuel, Mélanie Drilleau, Attilio Rivoldini, Zongbo Xu, Quancheng Huang, Raphaël F. Garcia, Vedran Lekić, Jessica C.E. Irving, James Bad "Geophysical evidence for an enriched molten silicate layer above the Martian core" by ro, Philippe H. Lognonné, James A.D. Connolly, Taichi Kawamura, Tamara Gudkova, and William B. Banerdt, October 25, 2023, Nature.
DOI:10.1038/s41586-023-06601-8
Compiled source: ScitechDaily