Unlike Earth's core, Mars' innermost layer cannot generate magnetic field
An artist’s depiction of the Martian interior and the paths taken by the seismic waves as they travelled through the planet’s core. Image: NASA / JPL and Nicholas Schmerr Mars’ innermost layer — the core — is likely in a liquid state. It is also smaller and denser than previously thought, according to a new study.
The Red Planet’s core is estimated to have a radius of approximately 1,780-1,810 kilometres, the study published in the journal PNAS stated. For comparison, the radii of the Earth’s liquid outer core and the solid inner core are 3,483 km and 1,220 km, respectively.
“Planetary cores are important because they can sometimes generate a planet-wide magnetic field (like on Earth). We’ve known for some time that Mars’ core does not do this,” Jessica Irving, senior lecturer in earth sciences at the University of Bristol and the study’s lead author, told Down To Earth.
An international group of researchers analysed seismic data from NASA’s InSight Mars Lander launched in May 2018. The American space agency retired the lander in December 2022 as it ran out of power.
“The InSight Mission to Mars put a seismometer (and other geophysical equipment) onto the surface of the planet to help learn more about the structure and composition of Mars,” Irving explained.
Seismometers pick up seismic waves — shockwaves generated after an earthquake. This helps researchers peer into Mars’ interiors and study its composition and properties.
Seismic waves behave differently as they pass through different materials. For example, they slow down when they traverse through liquid materials or hot regions.
“With InSight, we’re finally discovering what’s at the centre of Mars and what makes Mars so similar yet distinct from Earth,” Vedran Lekic, second author of the paper and associate professor of geology at the University of Maryland, said in a statement.
The team was specifically on the lookout for ‘farside’ seismic events, which occur on the opposite side of the planet to InSight.
They found two seismic events — one caused by a marsquake and the other by a large impact.
They then compared the time the waves took to pass through the core relative to seismic waves that stayed in the mantle.
The researchers then fed these measurements into computer models to predict the physical properties of the core, including its size.
They found that light elements, sulphur and oxygen, comprise a fifth of the core’s weight.
“Though both [Earth and Mars] are mostly made of iron, the core of Mars is less dense than that of Earth. Mars’ core contains more ‘light elements’ than Earth’s core,” Irwing explained.
This difference, she added, is due to multiple factors, including the material which congregated to form the planets.
“By learning more about the physical properties of Mars today, we provide data which could inform better models of how Earth and Mars formed,” she highlighted.
Further, the Earth’s magnetic field is generated in its outer liquid core. “The uniqueness of Earth’s core allows it to generate a magnetic field that protects us from solar winds, allowing us to keep water. Mars’ core does not generate this protective shield, and so the planet’s surface conditions are hostile to life,” Nicholas Schmerr, co-author of the paper and associate professor of geology at the University of Maryland, explained.
Mars, too, likely possessed a magnetic field in the past. It is also theorised that the Red Planet was once habitable before evolving to its current hostile state. The planet’s interiors, according to the researchers, could have played a key role in this evolution.
Though the Insight mission has been retired, researchers are still analysing the gathered data.
“Planetary seismologists are also excited about future missions to other parts of the solar system — we have had seismometers on Earth and the Moon, and there are other planets and moons which will be equally, if not more, exciting to study to understand how our solar system came to be as it is today,” Irwing said.
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