Geochemists have suspected that Mars has a solid inner core.

Mars, like Earth, has a liquid core. This has been confirmed by data from NASA's InSight probe operating on the surface of the Red Planet. It is likely that Mars' core is composed of molten iron mixed with lighter elements such as sulfur. According to calculations, the temperature in the planet's depths is too high for crystallization to occur. Nevertheless, scientists have synthesized an unusual iron sulfide that can transition to a solid state under specific conditions.

2025-02-26 10:01:08https://naked-science.ru/article/chemistry/geohimiki-zapodozrili

According to models, Mars' core is significantly more enriched with lighter elements compared to Earth's. This suggests that the process of planet formation from primordial material occurred differently.

Scientists lean towards the idea that Mars' iron core is alloyed with sulfur. There was an abundance of sulfur in the solar nebula from which our planetary system formed. During the differentiation of the planet's interior, sulfur exhibited an affinity for iron, and the core formation process occurred under conditions that were not sufficiently reducing and at high temperatures, preventing the concentration of other light elements, such as silicon or oxygen.

There is no direct evidence regarding the solidification of Mars' core, nor is there proof that it is completely liquid. Seismic observations have managed to detect the boundary between the mantle and the core, while density calculations indicate that the outer shell of the core is in a molten state. What lies deeper remains unclear. However, if an inner core exists, its radius is no more than 750 kilometers.

If we accept the hypothesis of a solid inner core, then the behavior of the Fe-FeS system plays a crucial role during the cooling and solidification process. Under certain conditions, either iron or its sulfides may begin to crystallize from the melt. The closer to the planet's center, the higher the likelihood of a phase rich in sulfur forming.

To test this, scientists from Germany, France, and Belgium conducted a series of laboratory experiments. The results are published in the journal Nature Communications.

The researchers synthesized a crystalline structure described by the formula Fe_4+xS₃ at pressures of nearly 15 gigapascals and a temperature of 1150 Kelvin. They then studied its composition, density, and potential role in the formation of a solid inner core.

According to calculations, the pressure at the center of Mars reaches 40 gigapascals, and the temperature is approximately 1970 Kelvin. Under these conditions, the refractory sulfide Fe_4+xS₃ is stable. However, if the temperature at the planet's center drops below 1960 Kelvin, the substance begins to crystallize.

This scenario suggests that the molten iron contains 17-25 percent sulfur by mass. If sulfur constitutes 7-12 percent by mass, then as the core cools, "iron flakes" should precipitate in its upper shell, which would re-melt as they sink towards the center.

This preliminary work indicates that modern Mars may have a solid inner core or that one may develop in the future as the interior cools. New experiments are needed to refine this hypothesis.