Mysterious Martian Core Smaller & Denser Than Previously Thought, Study Reveals

Recent research led by ETH Zurich scientists has unveiled surprising revelations about the inner workings of the red planet. The mission, which spanned four years and concluded in December 2022, exposed seismic secrets beneath the Martian surface.

New findings have offered a fresh, groundbreaking perspective on Mars' internal structure, specifically regarding the planet's Martian core.

The collaborative work has revealed that core possesses a significantly lower density than expected, with a surprisingly high proportion of light elements such as sulfur, carbon, oxygen and hydrogen, constituting around 20% of the core's weight.

The initial analyses, which left scientists puzzled as Earth's core is predominantly composed of iron, was made by a team of researchers with the ETH Zurich and the Institut de Physique de Globe de Paris. The findings were carried out with data collected by NASA's InSight lander, which recorded various marsquakes.

"This means that the average density of the Martian core is still somewhat low, but no longer inexplicable in the context of typical planet formation scenarios," says Paolo Sossi, assistant professor in the Department of Earth Sciences at ETH Zurich and member of the National Centres of Competence in Research (NCCRs) PlanetS.

The new revelations show the Martian core is smaller than initially estimated, reducing its radius from 1,800–1,850 kilometers to a range of 1,650–1,700 kilometers, representing about 50% of Mars' radius. This adjustment in size implies a higher density and, in turn, a reduced presence of light elements in the core, now estimated to be between 9 and 14% by weight.

The findings suggest the Martian core formed at an early stage in the planet's history, when the sun was still surrounded by a nebula gas rich in light elements. The research also benefited from seismometer data from marsquakes, particularly two quakes occurring on the opposite side of Mars in 2021, one of which was induced by a meteorite impact. The seismic events provided crucial information about the core and mantle structure.

"It took us a while to realize that the region we had previously considered to be the outer liquid iron core wasn't the core after all, but the deepest part of the mantle," explains Dongyang Huang, a postdoctoral researcher in the Department of Earth Sciences at ETH Zurich.

To determine the composition of the Martian core, scientists typically rely on comparing seismic data with synthetic iron alloys containing various proportions of light elements. However, these experiments are primarily designed for Earth's conditions and do not precisely mirror Mars' interior.

ETH Zurich researchers took an innovative approach, using supercomputer simulations and quantum-mechanical calculations to explore a wide range of alloy compositions. The calculations were then compared with measurements derived from InSight's seismic data.

Surprisingly, the researchers discovered the region previously assumed to be the outer liquid iron core was, in fact, the deepest part of Mars' mantle, composed of liquid silicates. This insight reshapes our understanding of the Martian internal structure and may help solve mysteries related to planet formation.

While InSight's mission ended, leaving questions unanswered, the data it collected will continue to yield insights for years to come, shedding light on the core of the red planet.

The findings of the study were published in the journal Nature.