A new study based on seismic data provided by NASA’s InSight lander offers a more comprehensive understanding of the deep interior of Mars and fresh insights into the differences between Earth, the third planet from the Sun, and Mars, the fourth planet.
Simulated interior of Mars and seismic waves passing through the planet’s core. Image: NASA
The study, announced with the first detection of seismic waves passing through the core of a non-Earth planet, reveals that the innermost layer of Mars is slightly smaller and denser than previously known. It also provides the best assessment to date of the composition of Mars’ core.
Both planets have cores consisting primarily of liquid iron. However, about 20% of Mars’ core is composed of lighter elements than iron, predominantly sulfur, along with oxygen, carbon, and a small amount of hydrogen.
This figure is nearly double the percentage of similar elements in Earth’s core, indicating that Mars’ core is significantly less dense than our planet’s core, though denser than the estimation from 2021 based on different data from InSight.
Jessica Irving, a seismologist at the University of Bristol in the UK, said, “The deepest regions of Earth and Mars have different compositions, which may be the product of both the conditions and processes as the planets formed and the materials that made them up.”
Irving is the lead author of the study published this week in the Proceedings of the National Academy of Sciences.
The study also refined the size of Mars’ core, indicating a diameter of about 3,560-3,620 km, which is about 20-50 km smaller than previous estimates. Mars’ core is slightly smaller than Earth’s core.
The nature of the core can play a decisive role in determining whether a rocky planet or moon can sustain life. For example, the core generates Earth’s magnetic field, which shields the planet from harmful cosmic radiation and the Sun.
Irving explained, “On planets and moons like Earth, there are outer silicate layers—rock—and a core made mostly of metal, iron. One of the most important ways that a core can affect habitability is by generating a planetary magnetic field.”
Earth’s core does this, but Mars’ core does not, although it may have done so billions of years ago. Mars’ core may no longer be convecting, filled with the necessary energy to generate such a field.
InSight lander on Mars. Image: NASA
Mars has a diameter of about 6,779 km, compared to Earth’s diameter of about 12,742 km, making Earth nearly seven times larger in overall volume.
The behavior of seismic waves passing through a planet can reveal details about its internal structure. The new discoveries stem from two seismic events occurring on the opposite side of Mars from the InSight lander—and specifically its seismometer—situated on the planet’s surface.
The first was an earthquake in August 2021 with its epicenter near Valles Marineris, the largest canyon in the Solar System. The second was a meteorite impact in September 2021, leaving behind a crater approximately 130 meters in diameter.
NASA officially retired the InSight mission in December of last year after four years of operations on Mars. Accumulated dust prevented InSight’s solar panels from recharging.
“The InSight mission has been tremendously successful in helping us decode the structure and conditions inside the red planet,” said Vedran Lekic, a geophysicist and co-author of the study from the University of Maryland.
“Deploying a network of seismometers on Mars would enable us to explore even further and understand this planet as a system, something that we cannot do by just looking at its surface from orbit,” Lekic added.