There seem to be many differences between Earth, the third planet from the sun, and its next-door neighbor Mars, the fourth, as a new study based on seismic data obtained by NASA's robotic InSight lander has offered a fuller understanding of the Martian deep interior and further details about dissimilarities between the two rocky worlds and their cores.
The research, informed by the first detection of seismic waves traveling through the core of a planet other than Earth, showed that the innermost layer of Mars is slightly smaller and denser than previously known. It also provided the best assessment of the Martian core composition to date.
Both planets possess cores comprised primarily of liquid iron. But the study found about 20% of the Martian heart is made up of elements lighter than iron – mostly sulfur, but also oxygen, carbon and a dash of hydrogen. That is about double the percentage of such aspects in Earth's core, meaning the Martian core is considerably less dense than our planet's core – though denser than a 2021 estimate based on a different type of data from the now-retired InSight.
"The deepest regions of Earth and Mars have different compositions – likely a product both of the conditions and processes at work when the planets formed and of the material they are made from," said seismologist Jessica Irving of the University of Bristol in England, lead author of the study published this week in the journal Proceedings of the National Academy of Sciences.
The study also refined the size of the Martian core, finding it has a diameter of about 3,560 to 3,620 kilometers (2,212 to 2,249 miles), approximately 20 to 50 kilometers smaller than previously estimated. As a result, the Martian core makes up a slightly smaller percentage of the planet's diameter than Earth.
The nature of the core can play a role in governing whether a rocky planet or moon could harbor life. The body, for instance, is instrumental in generating Earth's magnetic field that shields the world from harmful solar and cosmic particle radiation.
"On planets and moons like Earth, there are silicate – rocky – outer layers and an iron-dominated metallic core. One of the most important ways a core can impact habitability is to generate a planetary dynamo," Irving said.
"Earth's core does this, but Mars' core does not – though it used to, billions of years ago. As a result, Mars' core likely no longer has the energetic, turbulent motion needed to generate such a field," Irving added.
Mars has a diameter of about 6,779 kilometers, compared to Earth's about 12,742 kilometers, and Earth is almost seven times larger in total volume.
The behavior of seismic waves traveling through a planet can reveal details about its interior structure. The new findings stem from two seismic events on the opposite side of Mars, where the InSight lander – specifically its seismometer device – sat on the planet's surface.
The first was an August 2021 marsquake close to Valles Marineris, the largest solar system canyon. The second was a September 2021 meteorite impact that left a crater about 130 meters (425 feet).
The U.S. space agency formally retired InSight in December after four years of operations, with an accumulation of dust preventing its solar-powered batteries from recharging.
"The InSight mission has been fantastically successful in helping us decipher the structure and conditions of the planet's interior," University of Maryland geophysicist and study co-author Vedran Lekic said. "Deploying a network of seismometers on Mars would lead to even more discoveries and help us understand the planet as a system, which we cannot do by just looking at its surface from orbit."
