Mars’s Liquid Iron Core: New Insights from InSight Mission and Seismic Data
An analysis of Martian seismic data recorded by NASA’s InSight mission, combined with first-principles simulations of liquid metal alloys, has led researchers at ETH Zurich to discover that Mars’s liquid iron core is surrounded by a 150-kilometer thick layer of molten silicate. This finding indicates that the core is smaller and denser than previously believed. The reduced core radius implies a higher density than estimated earlier and suggests that the metal core consists of 9-15 wt% light elements, including S, C, O, and H.
After the successful completion of the NASA InSight mission, the analysis of marsquakes and computer simulations continues to provide new findings. The observed marsquakes show that the average density of the Martian core is significantly lower than that of pure liquid iron.
The radius of the Martian core has been reevaluated to be between 1,650 and 1,700 kilometers, smaller than the previously determined range of 1,800-1,850 kilometers. This discovery sheds light on the size and composition of Mars’s core, resolving a long-standing mystery.
Discovering Mars’s Interior: Insights from NASA’s InSight Lander
For four years, the NASA InSight lander detected and recorded marsquakes using its seismometer. Researchers from ETH Zurich collected and analyzed the data sent back to Earth to gain a better understanding of Mars’s internal structure. Senior Scientist Amir Khan from ETH Zurich remarks, “Although the mission officially ended in December 2022, our recent discovery has been quite fascinating.”
Mars’s Unique Silicate Layer
Through the analysis of recorded marsquakes and computer simulations, scientists have unveiled a new perspective on Mars’s interior. Sandwiched between the liquid iron alloy core and solid silicate mantle, there exists a 150-kilometer thick layer of liquid silicate or magma. “Unlike Earth, Mars possesses this distinct molten silicate layer,” says Khan.
This significant finding, recently published in the scientific journal Nature, aligns with a study led by Henri Samuel from the Institut de Physique de Globe de Paris that arrived at a similar conclusion through complementary methods. These discoveries provide valuable insights into the composition and size of Mars’s core, answering questions that have puzzled researchers for years.
Mars’s Core Composition
An analysis of marsquakes initially revealed that the average density of Mars’s core is considerably lower than that of pure liquid iron. In contrast, Earth’s core is primarily composed of approximately 90% iron by weight, while light elements such as sulfur, carbon, oxygen, and hydrogen make up about 10%.
Estimates of the Martian core’s density indicated a higher proportion of light elements, around 20% by weight. Until now, this result has been perplexing. Postdoctoral researcher Dongyang Huang from ETH Zurich explains, “The large amount of light elements seemed nearly impossible. We have been intrigued by this finding for some time.”
In their study published in Nature, researchers propose a new model for Mars’s internal structure. By analyzing seismic data captured after a meteorite impact, scientists from the NASA InSight mission suggest that Mars’s mantle is heterogeneous and consists of a layer of molten silicates atop the core. This groundbreaking model explains various geophysical observations and revolutionizes our understanding of Mars’s internal structure and its evolution.
Redefining the Martian Core
The revised radius of Mars’s core falls within the range of 1,650-1,700 kilometers, which represents about 50% of the planet’s overall radius. While smaller, the core still retains its mass, resulting in a higher density and a lower proportion of light elements. The new calculations estimate that the core contains between 9 and 14% light elements by weight.
As Professor Paolo Sossi from ETH Zurich states, “Although the average density of Mars’s core remains relatively low, it is now consistent with typical planet formation scenarios.” The presence of significant light elements suggests an early formation of the Martian core when the Sun was still surrounded by a gas nebula, allowing for the accumulation of light elements within the core.
Utilizing Distant Marsquakes
Initial calculations were based on marsquakes detected in close proximity to the InSight lander. However, in August and September 2021, the seismometer recorded two quakes on the opposite side of Mars, including one caused by a meteorite impact. Cecilia Duran, a doctoral student at ETH Zurich, explains, “These quakes generated seismic waves that passed through the core, providing us with valuable insights into its properties.”
In contrast, the earlier marsquakes reflected waves at the boundary between the core and mantle, offering limited information about Mars’s deep interior. With these new observations, researchers could determine the density and seismic wave speed of the fluid core up to a depth of approximately 1,000 kilometers.
Quantum-Mechanical Supercomputer Simulations
To determine the composition of the core material, scientists typically compare the data with synthetic iron alloys containing different proportions of light elements (S, C, O, and H). These alloys are subjected to high temperatures and pressures similar to those found within Mars, allowing for direct measurement of density and seismic wave speed.
However, current experiments mainly focus on conditions found within Earth’s interior and are not immediately applicable to Mars. Therefore, researchers at ETH Zurich employed quantum-mechanical calculations to compute the properties of various alloys. These calculations were carried out at the Swiss National Supercomputing Centre (CSCS) in Lugano, Switzerland.
When comparing the calculated profiles with measurements based on InSight seismic data, researchers encountered a challenge. It became apparent that no iron-light element alloy perfectly matched the data at both the core’s top and center. For instance, the iron alloy composition would require significantly more carbon than what was observed at the core-mantle boundary.
Researcher Huang explains, “It took us some time to realize that what we previously considered the outer liquid iron core was, in fact, the deepest region of the mantle.” Furthermore, comparing the density and seismic wave speed in the outermost 150 kilometers of the core showed consistency with those of liquid silicates, the solid material comprising Mars’s mantle.
Further analysis of previous marsquakes and additional computer simulations corroborated these findings. Unfortunately, limitations due to dusty solar panels prevented the InSight lander from providing more data to enhance our understanding of Mars’s interior composition and structure. Nevertheless, Khan remarks, “The InSight mission was a resounding success, providing us with invaluable data and insights that will be studied for years to come.”
For more information, refer to the article “NASA’s InSight Lander Uncovers Mars’s Molten Mystery.”
References:
“Evidence for a liquid silicate layer atop the Martian core” by A. Khan, D. Huang, C. Durán, P. A. Sossi, D. Giardini, and M. Murakami, Nature, October 25, 2023,doi.org/10.1038/s41586-023-06586-4
“Geophysical evidence for an enriched molten silicate layer above Mars’s core” by Henri Samuel, Mélanie Drilleau, Attilio Rivoldini, Zongbo Xu, Quancheng Huang, Raphaël F. Garcia, Vedran Lekić, Jessica C. E. Irving, James Badro, Philippe H. Lognonné, James A. D. Connolly, Taichi Kawamura, Tamara Gudkova, and William B. Banerdt, Nature, October 25, 2023,doi.org/10.1038/s41586-023-06601-8
The NASA Mars InSight Mission
The Jet Propulsion Laboratory (JPL) managed InSight for NASA’s Science Mission Directorate. InSight is part…
