In May 2022, the NASA InSight lander recorded a marsquake “monster” with a magnitude of -4.6. The event produced strong seismic waves that traveled across the surface of Mars.

Through continuous monitoring and with decreasing power levels on InSight’s seismometer, scientists at ETH Zurich gathered the data of a sizable marsquake. They found that the seismic waves traveled from the source of the earthquake to the measuring station and continued to travel around the entire planet several times.

In addition to providing information specific to Mars, the study also provides a global view of the planet. Researchers determined the global average thickness of the Martian crust based on the surface waves.

Doyeon Kim, a seismologist at the Institute of Geophysics at ETH Zurich, said: “From this earthquake, the largest earthquake recorded during the entire InSight mission, we observed surface waves circling Mars up to three times. The researchers measured how fast these waves propagate at different frequencies to get information about the structure where the waves went through.”

Scientists determined the thickness of the Martian crust by combining their newly obtained results with existing data on Mars’ gravity and topography. It is 42 to 56 kilometers (26 – 35 miles) on average. The crust is thinnest in the Isidis impact basin at ~10 km (6 mi) and thickest in Tharsis province at ~90 km (56 mi).

kim said, “This means that the crust of Mars is much thicker than that of the Earth or the Moon. In general, smaller planetary bodies in our solar system have thicker crusts than larger bodies. We were lucky enough to observe this earthquake. On Earth, we would struggle to determine the thickness of the Earth’s crust using the same earthquake that happened on Mars. Even though Mars is smaller than Earth, it transports seismic energy more efficiently.”

The study highlights the difference between the northern and southern hemispheres of Mars. On Mars, the Northern Hemisphere consists of low, flat terrain, while the Southern Hemisphere consists of high plateaus. A Martian dichotomy is the division between the northern and southern highlands.

Topographic map of the surface of Mars
Topographic map of the surface of Mars (l.) and display of the crust thickness (r.). (Illustration: MOLA Science Team / Doyeon Kim, ETH Zurich)

Kim said: “You might think that this difference can be explained by two different rock compositions. One stone would be denser than the other. While the composition may be the same in the north and south, the thickness of the crust varies. If the crust is thicker in the south, there would be less dense Martian mantle material underneath, while a thinner crust in the north would have more of this dense, heavier material.”

Scientists noted, “Based on the seismic observations and the gravity data, we show that the density of the crust in the northern lowlands and the southern highlands is similar.”

“The crust in the Southern Hemisphere, on the other hand, extends to a greater depth than in the Northern Hemisphere.”

“This finding is fascinating and puts an end to a long-standing scientific debate about the origin and structure of the Martian crust. After all, analysis of meteorite impacts on Mars last year already provided evidence that the crusts in the north and south are made of the same material. ”

kim said, “Our study shows how the planet generates heat and explains the thermal history of Mars. As a single-plate planet, the main source of heat produced in Mars’ interior today is the result of the decay of radioactive elements such as thorium, uranium and potassium. The study found 50 to 70 percent of these heat-producing elements in the Martian crust. This high accumulation could explain why there are local areas below that where melting processes can still occur today.”

Magazine reference:

  1. Doyeon Kim, Cecilia Duran, et al. Global crustal thickness revealed by surface waves orbiting Mars ESS Open Archive. 06 March 2023. DOI: 10.22541/essoar.167810298.85030230/v1