New results provide important insights into how Mars formed and evolved compared to Earth.

Groundbreaking research by the University of Bristol, published in the Proceedings of the National Academy of Sciences of the US, has provided unprecedented insights into the liquid core at the center of Mars. For the first time, sound waves, or seismic waves, have been detected traveling into the Martian core, providing vital information about the planet’s composition, formation, and evolution.

Despite encountering challenges such as Martian storms that hastened the accumulation of dust and reduced power to the NASA InSight Mars lander, the research mission extended its stay and collected geophysical data, including signals of marsquakes, until the end of last year. The measurements obtained from the seismic waves indicate that the liquid core of Mars is denser and smaller than previously believed, consisting of a mixture of iron and several other elements.

The study has shed new light on the planet’s formation and may even provide insight into how the red planet differs from Earth.

“The extra mission time certainly paid off,” remarks lead author Dr. Jessica Irving.

“We’ve made the very first observations of seismic waves travelling through the core of Mars. Two seismic signals, one from a very 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 travelling 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 being just a ball of iron, it also contains a large amount of sulfur, as well as other elements including a small amount of hydrogen.”

The researchers utilized data gathered by NASA’s InSight lander, a robotic spacecraft specifically designed to explore the interior of Mars. Equipped with a broadband seismometer, the lander was deployed on the Martian surface in 2018, enabling scientists to detect various seismic events, including marsquakes and meteorite impacts. With the help of a team of experts in fields such as seismology, geodynamics, and mineral physics, the researchers were able to analyze seismic waves traversing through Mars’ core and compare them to those in the shallower regions, ultimately allowing them to model the planet’s interior properties. To achieve this, the team utilized observations of two seismic events that occurred in the opposite hemisphere from the seismometer, measuring the travel times of seismic waves that passed through the core relative to those that remained in the mantle.

“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,” adds Dr. Irving. 

“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 all the way 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 seismic data collected from the InSight lander, the team constructed models that describe the physical properties of Mars’ core, including its size and elastic wave-speed. The models suggest that Mars’ core is slightly denser and smaller than previous estimates, with a radius of approximately 1,780-1,810 km.

These findings indicate that the core is composed of a relatively high fraction of light elements that are alloyed with iron, including abundant sulfur, as well as smaller amounts of oxygen, carbon, and hydrogen. These results shed new light on the formation and evolution of Mars and provide important insights into the planet’s interior structure.

“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,” adds Co-author Ved Lekic.

“We not only had to utilise 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.”

“The new results are important for understanding how Mars’ formation and evolution differ from those of Earth,” adds Dr. Irving.

“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.”

Source: 10.1073/pnas.2217090120 

Image Credit: NASA/JPL-Caltech