A University of Maryland professor’s research helped identify a previously unknown molten rock layer above Mars’ core in a paper published Oct. 25 in the scientific journal Nature, providing new insight into the red planet’s internal structure.
Vedran Lekić, a professor and the director of graduate studies in this university’s geology department, co-authored the paper with 13 other researchers from across the United States and Europe. The researchers used seismic data from NASA’s InSight mission to provide evidence of a molten layer around Mars’ liquid metal core. The researchers found that Mars’ core is smaller than previous estimates.
NASA’s InSight mission, which launched in 2018, used a seismometer to collect data on Mars’ seismic activity. Researchers used that data to analyze waves from marsquakes, or quakes that shake Mars’ surface, and work out the planet’s internal structures, according to associate geology professor Nicholas Schmerr, a participating scientist on the mission.
In September 2021, researchers detected an unusual marsquake triggered by a meteorite impact on the far side of the planet, Lekić said.
As seismic waves traveled through the planet after the impact, they vibrated along the top of the molten layer and radiated energy down to the core and back up along the molten layer before coming up through the surface, he said.
According to the paper’s lead author Henri Samuel, a researcher at the Paris Institute of Planetary Physics, the waves couldn’t be explained by a mantle with the same composition throughout.
“The travel time of those waves … was too slow to be explained by a purely homogeneous mantle,” Samuel said. “Everything started to look more in favor of the mantle layer scenario, because … the waves can travel through the layer but they get delayed significantly.”
The data backed up Samuel’s prediction that Mars has a heterogeneous mantle with a different chemical composition towards the center of the planet. Samuel said this particular layer above Mars’ core is rich in radioactive elements that produce heat when they decay and cause the layer to be molten.
The molten rock layer’s discovery also means the Martian core is denser and about 30 percent smaller than what researchers previously thought, Samuel said. The layer is about 150 kilometers or 90 miles thick, Lekić said.
“You can think of it as an ocean of molten rock,” Lekić said. “This layer at the base of Mars is going to be very rich in radioactive elements, and that means it’s going to stay hot.”
Lekić said the vigorous convection and rotation of liquid in the Earth’s outer core cools it down and generates the planet’s global magnetic field. But Mars’ core has “a heater on top,” as Lekić describes the molten layer, which prevents the core from cooling itself down. This could be why Mars doesn’t generate a magnetic field that surrounds the planet, Lekić noted.
“You have this hot blanket on top of the core which keeps the core nice and warm,” he said.
Mars’ magnetic field comes from magnetized rocks on the planet’s crust, according to NASA.
Earth’s magnetic field protects the planet by redirecting charged particles from solar winds to go around the planet, Lekić said. Since Mars doesn’t make its own magnetic field, charged particles slam into and strip away the Martian atmosphere, he added.
“We think that Mars lost a lot of its original atmosphere through this, it’s almost like erosion, but it’s happening by these charged particles that come out of the sun,” Lekić said.
Though InSight stopped collecting data after it ran out of power last year, Lekić and Schmerr said the data left unanswered questions to address in further research.
Schmerr said that while Earth has thousands of seismometers that allow scientists to map out its interior, InSight only used one, which made it harder to get the same level of detail for Mars.
“We’re still kind of blind where some of the activity on Mars might sit,” Schmerr said. “[A larger seismometer network is] something that would give us a better picture of where the seismicity is, and also tell us more about the deeper internal structure which tells us about the history and evolution of the planet.”