Mars has a liquid iron alloy core at its center. A new study presents the first observations of seismic waves propagating through the core of Mars. The research, led by the University of Bristol, used seismic data gathered by the InSight mission.
The measurements of these seismic waves indicate that the planet’s liquid core is slightly denser and smaller than previously thought and comprises a mixture of iron and numerous other elements.
Lead author Dr. Jessica Irving, Senior Lecturer in Earth Sciences at the University of Bristol, said: “The extra mission time certainly paid off. We’ve made the first observations of seismic waves traveling through the core of Mars. Two seismic signals, one from a distant marsquake and one from a meteorite impact on the far side of the planet, have allowed us to probe the Martian core with seismic waves. We’ve effectively been listening for energy traveling through the heart of another planet, and now we’ve heard it.”
“These first measurements of the elastic properties of Mars’ core have helped us investigate its composition. Rather than just a ball of iron, it also contains a large amount of sulfur, as well as other elements including a small amount of hydrogen.”
After obtaining data from NASA’s InSight lander, the team compared seismic waves traveling through the planet’s core with those transiting Mars’ shallower regions. They also modeled the properties of its interior.
In 2018, the InSight lander deployed a broadband seismometer on the Martian surface. The seismometer, since then, has recorded seismic events, including marsquakes and meteorite impacts.
The multidisciplinary team of researchers, which included seismologists, geodynamics, and mineral physicists, used observations of two seismic occurrences in the hemisphere opposite that of the seismometer to calculate the relative travel times of seismic waves that left the mantle and those that entered the core.
Dr. Irving said: “So-called ‘farside’ events, meaning those on the opposite side of the planet to InSight, are intrinsically harder to detect because a great deal of energy is lost or diverted away as waves travel through the planet. We needed both luck and skill to find and then use these events. We detected no farside events in the first Martian year of operations. If the mission had ended, then this research couldn’t have happened.
“The Sol 976 marsquake was the most distant event found during the mission. The second farside event, S1000a — the first event detected on day 1,000 of operations — was particularly useful because it turned out to be a meteorite impact which we heard through the planet, so we knew where the seismic signals came from. These events came after the Marsquake Service (MQS) had honed their skills on hundreds of days of Martian data; it then took a lot of seismological expertise from across the Insight Team to tease the signals out from the complex seismograms recorded by the lander.”
Using these measurements, scientists built models describing the physical properties of the core, including its size and elastic wave speed. The findings showed that Mars’ core has a radius of roughly 1,780-1,810 km and is slightly denser and smaller than previously thought. These results are consistent with the core containing a relatively high fraction of light elements alloyed with iron. These light elements include a lot of sulfur and relatively little oxygen, carbon, and hydrogen.
Co-author Ved Lekic, Associate Professor of Geology at the University of Maryland College Park, in the US, said: “Detecting and understanding waves that travel through the very core of another planet is incredibly challenging, reflecting decades of efforts by hundreds of scientists and engineers from multiple countries. We not only had to utilize sophisticated seismic analysis techniques but also deploy knowledge of how high pressures and temperatures affect properties of metal alloys, leveraging the expertise of the InSight Team.”
Dr. Irving added: “The new results are important for understanding how Mars’ formation and evolution differ from those of Earth. New theories about the formation conditions and building blocks of the red planet will need to be able to match the core’s physical properties as revealed by this new study.”
- Jessica C. E. Irving, Vedran Lekić, Cecilia Durán et al. First observations of core-transiting seismic phases on Mars. Proceedings of the National Academy of Sciences, 2023; 120 (18) DOI: 10.1073/pnas.2217090120