– The red planet is thin-skinned and has a soft core
Under the auspices of ETH Zurich, researchers have studied the inner workings of our neighboring planet. They want to understand why Mars evolved so differently from Earth.
As NASA’s Persevering Mars rover prepares to take surface rock samples, Insight is looking deeper. The projectile landed near the Martian equator in November 2018. At the beginning of 2019, the Insight seismic sensor, which ETH Zurich helped develop, placed its ear in Martian soil.
Similar to a doctor carrying a stethoscope with a patient, the Seismic Experiment of the Endoskeleton (Seis) listens to the interior of Mars. To do this, it records accurate seismic signals: the dome-shaped detector has now recorded more than 1,000 earthquakes for Mars.
Several international research teams, led by ETH Zurich, are now reporting what these signals tell about the interior of Mars. Simply put, Mars has an unexpectedly thin crust, a solid top that is somewhat thicker than the mantle, and a core much larger and lighter than expected. Three articles were published in the journal Science detailing the details.
Could a fate similar to that of Mars threaten Earth?
«Obwohl Mars und Erde bei ihrer Entstehung recht ähnliche Himmelskörper waren, hat der Mars eine ganz andere Entwicklung durchgemacht als die Erde», sagt Domenico Giardini, Professor für Seismologie und Geodynamik Züdynamik an derende eden et ETHite he is. “Ultimately, we want to better understand why this happened and whether Earth could face a fate similar to that of Mars.”
As Giardini says, the researchers had to move forward with their studies like a hilarious treasure hunt: they first had to find the first stop. This contained information about Mars’ mantle and information on the way to the second station: the planet’s core. etc. The treasure to be recovered is to understand the origin and evolution of the red planet.
It was the big first stage, ever JTo learn more about the basic structures of Mars. Researchers were able to detect the most powerful earthquakesWhy It detects only so-called sky waves that travel into the interior of Mars. When the structure changes, the space waves are reflected and partially reach the surface with Seis. However, these powerful earthquakes did not give rise to the so-called surface waves. Researchers doubt whyInside and researchers The earthquakes are very weak and very deep. This means that an important source of information was missing: only by combining these two types of waves could JGiving more accurate information about the speed of wave propagation and the properties of the inner layers of Mars.
Earthquake echo as an important source of information
“It took us over a year to solve this problem,” Giardini says. It consisted of examining nearly a dozen of the 43 strong deep Mars earthquakes recorded so far with the clearest signals. Because it was reflected back and forth like an echo several times between the internal structures of Mars and the surface of Mars. “From these echoes, we were able to extract information about the velocity of diffusion and thus about the chemistry and temperature of the envelope,” says Amir Khan, senior author of the related book. a study. Khan conducts research at both ETH and the University of Zurich.
That was the first stop in the treasure hunt. It provided information about the mantle structure to a depth of about 800 km. Down to a depth of 500 kmn Therefore the mantle is very rigid and therefore belongs to the so-called lithosphere of the planet. K says. “In general, the mantle of Mars is a simpler version of the mantle of the Earth”hat. “Above the deepest mantle to a depth of about 1,500 kmn But we still know a little.”
Once we know how fast waves propagate in the mantle, the researchers were able to do just thatWhy Specifically looking for waves that are reflected from the heart. To do this, they searched for special space waves, called shear waves. These cannot diffuse into liquids. Therefore, it does not penetrate into a liquid planetary core. The core of Mars was expected to consist of liquid iron and nickel. “Now we know for sure,” Giardini says.
Why do light elements such as sulfur and hydrogen contaminate the core?
The radius of the core is about 1,830 kilometers, say researchers «Science» to report. That’s just over half the distance from the surface to the center of the planet – a similar volume ratio between the core and the whole planet as with Earth. This means that the core of Mars is, firstly, larger, and secondly, much lighter than expected. This means: “In addition to heavy elements such as iron and nickel, lighter elements such as sulfur, carbon, oxygen and hydrogen must also be present in the core,” says Simon Stehler of the Institute of Geophysics at ETH Zurich, lead author of the basic study. The big question now is: How can these light elements “contaminate” the core? According to Shettler, part of the explanation is that Mars formed before Earth and from different materials.
Provides liquid planetary core to scientistsinside and world He still faces another mystery: This must generate a magnetic field. “The magnetic field on Mars has been very active for about a billion years,” Giardini says. Then he disappeared. We do not knowAnd the Why.”
Researchers are now looking for signals from earthquakes on the other side of the planet, whose waves penetrate the core, in order to learn more about them. Because the absence of a magnetic field is the deciding factor that distinguishes Mars from Earth: without a magnetic field there is no protection from the solar wind. This gradually blew up the Martian atmosphere into space and weakened it considerably.
the third a study orbiting the crust of Mars. To this end, researchers working with Brigitte Knappmayr-Andron of the Pennsberg Seismological Station at the University of Cologne have examined fairly weak earthquakes with high-frequency signals. Their origin lies at a shallow depth in the crust of Mars. These tremors are literally trapped in the cortex and spread almost without relief.
Studies help to better understand other planets and exoplanets
“The cortex has been shown to be much thinner than expected,” says Giardini, who is also involved in this study. It is between 24 and 45 kilometers thickn On. The models were between 30 and 90 kilometersn I suggested.
“These three studies severely limit the potential internal structures of Mars today,” San Cottar and Paula Collière of the University of Cambridge wrote in another study. «Science» published a toolPresentation of the three studies. “This improves our understanding of how the planet formed billions of years ago and how it evolved over time.” According to Shettler, current studies are very useful for validating models of planet formation. “It helps us understand other Earth-like planets or exoplanets, which we can’t land on and turn on the seismometer.”
Another station to be found, according to Giardini, is the precise distribution of water. Events are known at the poles. However, it is unclear what depths and amounts of water are in the interior of Mars. “Here too, we first have to clarify one question before we can address the next,” Giardini says. Just like searching for treasure.