Unravel the basic mystery of the Red Planet

Analysis of Martian seismic data recorded by the InSight mission, as well as first-principles simulations of the seismic properties of liquid metal alloys, revealed that Mars’ liquid iron core is surrounded by a molten silicate layer 150 kilometers thick and, as a result, the core is smaller than previously suggested. The decrease in core radius indicates a higher density than previously estimated, and is consistent with a metallic core consisting of 9–15 wt% light elements, mainly S, C, O, and H. Credit: Thibaut Roger, NCCR PlanetS, ETH Zurich

MarsThe liquid iron core is smaller and denser than previously thought. Not only are they smaller, but they are also surrounded by a layer of molten rock. This is what ETH Zurich researchers concluded on the basis of seismic data from the InSight lander.

• One year after NASA The InSight mission has ended, and analysis of recorded Martian earthquakes, combined with computer simulations, continues to yield new results.
• Analysis of the initially observed Martian earthquakes shows that the average density of the Martian core must have been much lower than the density of pure liquid iron.
• New observations show that the radius of Mars’ core has decreased from the initially determined range of 1,800-1,850 kilometers to 1,650-1,700 kilometers.

Discovering the interior of Mars: Insights from NASA’s InSight Lander

For four years, NASA’s InSight lander recorded tremors on Mars using its seismometer. Researchers at ETH Zurich collected and analyzed data sent back to Earth to determine the planet’s internal structure. “Although the mission ended in December 2022, we have now discovered something very interesting,” says Amir Khan, a senior scientist in the Department of Earth Sciences at ETH Zurich.

The unique silicate layer of Mars

Analysis of recorded Martian earthquakes, combined with computer simulations, paints a new picture of the planet’s interior. Trapped between liquid Martian iron Alloy The planet’s core and solid silicate mantle lie in a layer of liquid silicate (magma) about 150 kilometers thick. “The Earth doesn’t have a completely molten silicate layer like this,” Khan says.

This result, now published in the scientific journal nature Together with a study by Henri Samuel, of the Institut Physique du Monde in Paris, which reached a similar conclusion using complementary methods, it also provides new information on the size and composition of the Martian core, solving a mystery that researchers had previously solved. So far He couldn’t explain.

Basic composition of Mars

Analysis of the initially observed Martian earthquakes showed that the average density of the Martian core must have been much lower than the density of pure liquid iron. For example, the Earth’s core is made up of about 90% of its weight in iron. Light elements such as sulfur, carbon, oxygen, and hydrogen make up a total of about 10 percent by weight.

Initial estimates of the density of the Martian core showed that it was composed of a much larger proportion of light elements – about 20% by weight. “This represents a very large group of light elements, which is close to impossible. We have been wondering about this result ever since,” says Dongyang Huang, a postdoctoral researcher in the Department of Geosciences at ETH Zurich.

Henry Samuel, a researcher at the National Center for Scientific Research and a geodynamicist at IPGP, explains the new model for the internal structure of Mars, proposed in an article published in the journal Nature. The study, conducted by scientists from NASA’s InSight mission, suggests that the Martian mantle is heterogeneous and consists of a layer of molten silicates covering the Martian core. This model, built using seismic data recorded on Mars after a meteorite impact, which accounts for all geophysical observations, revolutionizes our view of the Red Planet’s internal structure and evolution. Credit: © IPGP

Redefining the essence of Mars

The new observations show that the radius of the Martian core has decreased from the initially determined range of 1800-1850 km to 1650-1700 km, which represents about 50% of the Martian radius. If the Martian core is smaller than previously thought but has the same mass, it means it has a greater density and therefore contains fewer light elements. According to new calculations, the proportion of light elements has decreased to between 9 and 14 percent by weight.

“This means that the average density of the Martian core is still fairly low, but it is no longer unexplainable in the context of typical planet formation scenarios,” says Paolo Susi, associate professor in the Department of Earth Sciences at ETH Zurich and a member of the National Geosciences Commission. Centers of Competence in Research (NCCRs) PlanetS.

The fact that the Martian core contains a large amount of light elements indicates that it formed very early, perhaps when the Sun was still surrounded by nebula gas from which light elements could have accumulated in the Martian core.

Taking advantage of distant Martian earthquakes

Initial calculations were based on tremors that occurred close to the InSight lander. But in August and September 2021, the seismograph recorded two earthquakes on the other side of Mars. One of them was due to a meteorite impact.

“These earthquakes produced seismic waves that traversed the core of the Earth,” explains Cecilia Duran, a doctoral student in the Department of Geosciences at ETH Zurich. “This allowed us to illuminate the heart.”

In contrast, in the case of previous Martian earthquakes, the waves were reflected at the core-mantle boundary, providing no information about the red planet’s deepest interior. As a result of these new observations, researchers have now been able to determine the density and speed of seismic waves of the liquid core down to a depth of about 1,000 kilometers.

Quantum mechanical supercomputer simulation

To infer the material composition from these profiles, researchers typically compare the data with synthetic iron alloys containing different proportions of light elements (S, C, O, and H). In the laboratory, these alloys are exposed to high temperatures and pressures equivalent to those found in the interior of Mars, allowing researchers to directly measure the density and speed of seismic waves.

However, at the moment, most experiments are performed in conditions prevailing in the Earth’s interior, and therefore are not immediately applicable to Mars. As a result, researchers at ETH Zurich turned to a different approach. They calculated the properties of a wide range of alloys using quantum mechanical calculations, which they conducted at the Swiss National Supercomputing Center (CSCS) in Lugano, Switzerland.

When the researchers compared the calculated profiles with their measurements based on InSight seismic data, they ran into a problem. It turns out that there are no light iron alloys that simultaneously match the data at the top and center of Mars. For example, at the boundary between the core and mantle, the iron alloy should have contained much more carbon than is found in the interior of the core.

“It took us some time to realize that the region we had previously considered to be the outer liquid iron core was not the core after all, but the deepest part of the mantle,” Huang explains. In support of this, the researchers also found that the density and speed of seismic waves measured and calculated in the farthest 150 kilometers of Mars’ core were consistent with those found in liquid silicates – the same material, in solid form, that makes up Mars’ mantle. .

Further analysis of previous Martian earthquakes and additional computer simulations confirmed this finding. Unfortunately, dusty solar panels and resulting power shortages made it impossible for the InSight lander to provide additional data that could have shed more light on the composition and structure of Mars’ interior. “However, InSight was a very successful mission, providing us with a lot of new data and insights that will be analyzed for years to come,” Khan says.

For more information about this study, see NASA’s InSight Lander Reveals the Mystery of Molten Mars.

References:

“Evidence for a liquid silicate layer above the core of Mars” by A. Khan, D. Huang, C. Durán, P. A. Sossi, D. Giardini and M. Murakami, October 25, 2023, nature.
doi: 10.1038/s41586-023-06586-4

“Geophysical evidence for a rich molten silicate layer above the core of Mars” by Henry Samuel, Melanie Drilio, Attilio Rivoldini, Zhongbo Xu, Quanqing Huang, Rafael F. Garcia, Vedran Lekic, Jessica C. E. Irving, James Padro, Philip H. Lugnonier, James Connolly , Taichi Kawamura, Tamara Gudkova, and William B. Bannerd, October 25, 2023, nature.
doi: 10.1038/s41586-023-06601-8

NASA’s Mars Insight mission

jet propulsion laboratory (Jet Propulsion Laboratory) managed InSight for NASA’s Science Mission Directorate. InSight is part of NASA’s Discovery Program, managed by the agency’s Marshall Space Flight Center. Lockheed Martin Space built the InSight spacecraft, including the cruise platform and lander, and supported spacecraft operations for the mission.

A number of European partners, including the French National Center for Space Studies (CNES) and the German Aerospace Center (DLR), are supporting the InSight mission. The French National Center for Space Studies presented the Seismic Experiment for Interior Structure (SEIS) instrument to NASA, with the principal investigator at the IPGP (Institut Physique du Générale in Paris). Significant contributions to SEIS came from the IPGP; the Max Planck Institute for Solar System Research (MPS) in Germany; the Swiss Federal Institute of Technology (ETH Zurich) in Switzerland; Imperial College London University of Oxford in the United Kingdom; And the Jet Propulsion Laboratory. The Marsquake service is led by ETH Zurich, with significant contributions from IPGP; the University of Bristol; Imperial College; ISAE (Higher Institute of Aviation and Space); MPS. And the Jet Propulsion Laboratory. The Heat Flow and Physical Properties Package (HP3) instrument was provided by DLR, with major contributions from the Space Research Center (CBK) of the Polish Academy of Sciences and Astronica in Poland. The Spanish Center for Astrobiology (CAB) supplied the temperature and wind sensors.