The crust, mantle and core of Mars are very different from those of Earth

Researchers used seismic data to look inside Mars for the first time.

They measured the crust, mantle and core and reduced their composition. The three resulting articles (first, second, third) appear together as a cover story in the newspaper Science.

Since early 2019, researchers have been recording and analyzing earthquakes as part of the InSight mission. This is based on a seismometer whose electronics for data acquisition and control were developed at ETH Zurich. Data that will determine the formation and evolution of Mars and, by extension, the entire solar system.

We know the Earth is made up of shells: a thin, light, solid crust of rock surrounds a thick mantle of heavy, viscous rock, which in turn envelops a core made up mostly of iron and nickel. Terrestrial planets, including Mars, were believed to have a similar structure.

“Now, the seismic data has confirmed that Mars was probably once completely melted before it split into the crust, mantle and core that we see today, but that they are different from those on Earth,” Amir explains. Khan, scientist at the Institute of Geophysics at ETH Zurich. and at the Institute of Physics of the University of Zurich. He and his colleague Simon Stähler analyzed data from NASA’s InSight mission, in which ETH Zurich is participating under the leadership of Professor Domenico Giardini.

The crust, mantle and core of Mars

The researchers found that the Martian crust below the probe’s landing site near the Martian equator is between 15 and 47 kilometers (9.3-29 miles) thick. Such a thin crust must contain a relatively high proportion of radioactive elements, which calls into question previous models of the chemical composition of the entire crust.

Below the crust is the mantle with the more solid rock lithosphere reaching 400 to 600 kilometers deep, twice as deep as on Earth. This could be because there is now only one continental plate on Mars, unlike Earth with its seven large moving plates. “The thick lithosphere fits well with the model of Mars as a ‘single plate planet’,” Khan concludes.

The measurements also show that the Martian mantle is mineralogically similar to the Earth’s upper mantle. “In this sense, the Martian mantle is a simpler version of the Earth’s mantle.” But seismology also reveals differences in chemical composition. The Martian mantle, for example, contains more iron than that of the Earth. However, theories about the complexity of the Martian mantle stratification also depend on the size of the underlying core – and here, too, the researchers came to new conclusions.

The Martian core has a radius of about 1,840 kilometers (1,143 miles), which is 200 kilometers (124 miles) longer than assumed 15 years ago when the InSight mission was planned. .

“After determining the radius of the nucleus, we can now calculate its density,” says Stähler.

“If the radius of the nucleus is large, the density of the nucleus must be relatively low,” he explains: “This means that the nucleus must contain a large proportion of lighter elements in addition to iron and nickel. These include sulfur, oxygen, carbon and hydrogen, and constitute a surprisingly high proportion. The researchers conclude that the makeup of the entire planet is not yet fully understood. Nonetheless, ongoing investigations confirm that the nucleus is liquid – as it is suspected – even though Mars no longer has a magnetic field.

Mars earthquake data

The researchers obtained the new results by analyzing various seismic waves generated by earthquakes. “We could already see different waves in the InSight data, so we knew how far away from the lander these earthquake epicenters were on Mars,” says Giardini.

To be able to say anything about the internal structure of a planet requires earthquake waves that are reflected at or below the surface or at the heart. Today, for the first time, researchers have successfully observed and analyzed such waves on Mars.

“The InSight mission was a unique opportunity to capture this data,” says Giardini. The data stream will end in a year when the solar cells in the lander are no longer able to produce enough power. “But we are far from having finished analyzing all the data – Mars still presents us with many mysteries, especially if it was formed at the same time and from the same material as our Earth.”

It is especially important to understand how the internal dynamics of Mars caused it to lose its active magnetic field and all surface water. “This will give us an idea of ​​if and how these processes could occur on our planet,” explains Giardini. “That’s the reason we’re on Mars, to study its anatomy.”

Source: ETH Zurich

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