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

In May 2022, a powerful earthquake on Mars, during which seismic wavesseismic waves orbited the Martian surface up to three times, enabled ETH Zurich researchers to determine the overall thickness and density of the planet’s crust. With a sizesize estimated at 4.6, this earthquake is the most powerful ever observed on another planet. It was measured by Six seismometers aboard Insight, whose mission to Mars was completed in December 2022 after being in operation for four years.

The surface waves observed during this large earthquake did not only travel from the source to 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 on Mars. They also allowed get an overview of the planet “says Doyeon Kim, seismologistseismologist at the Department of Geophysics at ETH Zurich. To get information about the structure that the waves pass through, the researchers measured speedspeed propagation of these waves at different frequenciesfrequencies with the result a ” overview of the internal structure at different depths » and information about « Martian crust, which appears much thicker than Earth’s crustEarth’s crust or moon, and the main source of heatheat of the planet is radioactive “, emphasizes the seismologist and lead author of a study that has just been published in review Geophysical Research Letters. Earlier, waves surfaces observed during the two major meteorite impacts also made it possible to obtain results along their specific propagation trajectories, but regional and not global as today.

The crust of Mars is much thicker than that of the Earth or the Moon

By combining their new findings 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 Isidis 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 findings of this research concerns the difference between northern hemispheresnorthern hemispheres, which consists of flat lowlands, and the 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, one rock being 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 the crust in contrastsouthern 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 thoriumthoriumI’uraniumuranium and potassium “. The study showed that 50-70% of these heat-producing elements found in the Martian crust, so this strong accumulation may explain why there are local areas beneath the crust where processes of meltingmelting can still take place today “.