HEFEI -- Chinese and international scientists have, for the first time, discovered a solid inner core, with a radius of about 600 km, inside Mars, thereby providing crucial clues to the evolutionary history of Mars' magnetic field.

As the terrestrial planet in the solar system with an environment most similar to Earth, Mars has often been a key subject in studying internal planetary structure and evolution, as well as being one of the core targets in deep space exploration.

However, probing the deep structures of planets has always been challenging. Taking Earth, with which we are most familiar, as an example, scientists first inferred the existence of Earth's inner core through seismic waves in 1936 -- but it took nearly half a century to confirm the existence of its solid inner core.

In comparison, exploring the internal structure of Mars is even more difficult. So far, although thousands of marsquakes have been recorded, issues such as weak signals and noise interference have severely limited the study of Mars' deep structure.

A team led by Sun Daoyuan and Mao Zhu from the University of Science and Technology of China, located in east China's Anhui Province, in collaboration with an international researcher, conducted an in-depth analysis of marsquake data recorded by NASA's InSight lander. They applied array analysis methods to marsquake data and successfully extracted key seismic phases passing through Mars' core by analyzing data from 23 marsquake events with relatively high signal-to-noise ratios.

According to a paper published Wednesday in the journal Nature, the results of this experiment indicate that Mars' core has a layered structure -- with an outer liquid core and a deeper solid inner core featuring higher seismic wave velocities.

The team measured the radius of Mars' solid inner core to be around 600 kilometers, accounting for about one-fifth of Mars' total radius. If Mars were scaled up to the size of Earth, the structural proportion of its inner and outer cores would be highly similar to Earth's.

Additionally, marsquake data revealed an approximately 30-percent jump in wave velocity and a 7 percent difference in density between Mars' outer and inner cores. Based on these findings, the team further analyzed the mineral composition of the inner core.

The results show that Mars' core is not composed solely of iron and nickel but may also contain 12 to 16 percent of sulfur, 6.7 to 9 percent oxygen, and no more than 3.8 percent of carbon.

This type of planetary core structure containing light elements not only provides important clues to the evolutionary history of Mars' magnetic field from its early activity to its current silence, but also lays a critical foundation for comparing the internal evolutionary differences between Earth and other terrestrial planets, according the study.

The study is the first of its kind to confirm the existence of a solid inner core in a planet other than Earth -- demonstrating that Mars has a core-mantle differentiation structure similar to Earth's.

The innovative method using Martian seismology developed in this study also provides an important reference for future missions, such as lunar exploration, in employing seismological methods to probe the deep structures of celestial bodies.

"The authors have done a detailed job of using multiple working lines of evidence for their phase detection analysis. Martian seismology is notably tough, so congratulations to the authors for doing such a thorough and careful job," the journal's reviewer commented.