Marsquakes and meteorite hits show Mars has a dense liquid metal core

Mars has a heavy heart after all.

The Red Planet has a dense core of liquid iron surrounded by a relatively thin layer of molten rock, researchers report. The finding resolves a recent conundrum that came about when seismic measurements on Mars seemed to suggest that the planet had a surprisingly large, light core rich in low-density elements (SN: 4/24/23).

The new view, described in two studies in the Oct. 26 Nature, shows the planet is made of materials common in the solar system at the time Mars formed. A lighter core would have required a mix of elements that wouldn’t have matched the proportions in the dust and debris that eventually became the solar system.

The researchers deduced the structure of Mars’ interior by studying seismic waves detected with NASA’s InSight lander (SN: 2/24/20). It measured Marsquakes and reverberations from meteorite impacts on the planet for a little over four years.

Waves reflecting from the molten rock layer were initially interpreted as bouncing from the outer edge of a core with a radius of about 1,800 kilometers and a density of 6,200 kilograms per cubic meter. The new research added data from seismic waves that dip into that molten layer to reveal the planet’s true heart.

The core has a roughly 10 percent smaller radius and a higher density than previously reported, with one group finding a density of 6,650 kilograms per cubic meter, and the other finding 6,500 kilograms per cubic meter. 

A better understanding of Mars has implications far beyond the Red Planet. Mars and Earth were very similar when they first formed, says planetary scientist Henri Samuel of CNRS in Paris, and a coauthor of one of the new studies. “However, at some point these two planets diverged and Mars is now not habitable while the Earth is. Therefore, understanding how this divergence has occurred can tell us a lot [about] our own planet.”