An earthquake on Mars reveals the amazing features of the Martian crust

In May 2022, a strong earthquake on Mars, during which seismic wavesseismic waves circled the Martian surface up to three times, allowed ETH Zurich researchers to determine the overall thickness and density of the planet’s crust. With a magnitudemagnitude estimated at 4.6, this earthquake is the strongest ever observed on another planet. It was measured by the Seis seismometer aboard Insight, whose mission to Mars ended in December 2022 after operating for four years.

The surface waves observed during this large earthquake not only traveled from the source of the earthquakeearthquake to the measuring station, but they also continued to circumnavigate the planet several times. These data did not only provide information about specific areas of Mars. They also allowed get an overview of the planet “says Doyeon Kim, seismologistseismologist at the Institute of Geophysics of ETH Zurich. In order to obtain information on the structure traversed by the waves, the researchers measured the vitessevitesse propagation of these waves at different frequenciesfrequencies with the result a ” overview of the interior structure at different depths » and information on the « Martian crust which appears much thicker than the Earth’s crustEarth’s crust or lunar, and the main source of heatheat of the planet is radioactive “, underlines the seismologist and main author of a study which has just been published in the journal Geophysical Research Letters. Previously, the surface waves observed during the two large meteorite impacts also provided results along their specific propagation paths, but regional and not global as today.

The Martian crust much thicker than that of the Earth or the Moon

By combining their new results with existing data on Mars’ gravity and topography, the researchers were able to determine the thickness of the Martian crust, ” on average from 42 to 56 kilometers “. They were able to measure that this crust is on average “ thinnest at the Isidis impact basin, ~10 km, and thickest in Tharsis Province, ~90 km “. To put this into perspective, seismic data indicate that the Earth’s crust has an average thickness of 21 to 27 kilometers, while the lunar crust, as determined by the mission’s seismometers ApolloApollohas a thickness between 34 and 43 kilometers.

One of the most important results of this research concerns the difference between northern hemispheresnorthern hemispheres, made up of flat lowlands, and south, with its high plateaus. The division between the northern lands, at very low altitudes, and the southern highlands is called the Martian dichotomy. As Doyeon Kim explains, “ one might think that this difference is explained by two different rock compositions, with one rock denser than the other “. But, surprisingly, this is not the case. Based on seismic observations and gravity data, the researchers showed that the ” density of the crust in the northern lowlands and the southern highlands is similar but that in contrast, the crust in thesouthern hemispheresouthern hemisphere extends to a greater depth than in the northern hemisphere ». « This discovery is very interesting and puts an end to a long-standing scientific discussion about the origin and structure of the Martian crust. “says Doyeon Kim.

Finally, other conclusions can also be drawn from the thickness of the Martian crust of which ” how the planet generates its heat and explains the thermal history of Mars “. As a single-plate planet, the main source of heat produced inside Mars today is ” the result of the decay of radioactive elements such as thoriumthoriuml’uraniumuranium and potassium “. The study found that 50-70% of these heat-producing elements are found in the Martian crust, so this strong accumulation could explain why there are local regions under the crust where processes of sourcesource can still take place today ».