NASA's InSight probe is out of service, but with the help of its collected data, a research team has now been able to determine how thick the crust of Mars is.
Zurich – Researchers at ETH Zurich had to wait more than three years before the seismometer of NASA's InSight spacecraft measured a particularly severe earthquake on Mars. With an estimated magnitude of 4.6, it was the most severe quake recorded on Mars to date. Larger ones will no longer be measured, at least by "InSight" – the Nasa probe has been out of service for some time. For a research team led by seismologist Doyeon Kim from the Institute of Geophysics at ETH Zurich, however, the quake was a stroke of luck.
"This marsquake sent out strong seismic waves that moved along the surface of Mars," Kim said in a statement. "From this largest quake recorded during the entire 'InSight' mission, we observed surface waves orbiting Mars up to three times," says the first author of a study published in the journal Geophysical Research Letters. The researchers were able to measure how fast the seismic waves propagate at different frequencies and thus learn more about the internal structure of Mars.
Martian crust is thicker than Earth's crust
By combining the new results with existing data on Mars, the research team was able to determine the thickness of the Martian crust: it averages 42 to 56 kilometres. The thinnest crust exists in the Isidis Plain (10 kilometers), the thickest crust is in the province of Tharsis (90 kilometers). In comparison, the Earth's crust is much thinner, as other researchers have also calculated with the help of seismic data: it is 21 to 27 kilometers thick. The moon's crust was calculated using seismometers from the "Apollo" missions – it has a thickness of between 34 and 43 kilometres.
Mars: These rovers and space probes explore the red planet
Mars: These rovers and space probes explore the red planet
"This makes the Martian crust much thicker than the crust of the Earth or the Moon," Kim notes. One of his team's most important research findings is the difference between the northern and southern hemispheres of Mars. While the north consists of flat lowlands, in the south there are high mountains – the so-called Martian dichotomy. Kim's research team was able to prove that the crust is similar in the northern lowlands and in the southern highlands. However, the crust in the south reaches a greater depth than in the northern hemisphere. "This finding is exciting and allows us to end a long-standing scientific discussion about the origin and structure of the Martian crust," Kim said.
Mars generates heat by decay of radioactive material
From the thickness of the Martian crust, the research team was also able to draw conclusions about how Mars generates heat and how it evolved thermally. According to the study, Mars generates heat in its interior primarily through the decay of radioactive elements such as thorium, uranium and potassium. What sounds exotic, however, is not at all: Heat is also generated in the interior of the earth by the decay of radioactive isotopes, among other things. (tab)