NASA’s InSight lander offers unprecedented glimpse into the bowels of Mars

For the first time, we know what the interior of another planet similar to ours looks like. In a trio of studies published Thursday, July 22 in the journal Science, an international team of more than 40 scientists revealed how the core, mantle and crust of Mars contrast with those of Earth.

By analyzing seismic data collected by NASA’s InSight lander on the Red Planet, the researchers estimated the size of Mars’ core, the thickness of its crust, and the composition of its mantle (the middle layer). “We only have this kind of information for the Earth and the moon,” Brigitte Knapmeyer-Endrun, a planetary seismologist at the University of Cologne and co-author of the new research, told Insider. “But the Moon, we can’t compare it very well to the Earth because it is much smaller.”

Read also – We know a little more about the presence of methane on Mars

Mars, however, is our smaller terrestrial twin. The new studies suggest that its core is less dense than that of Earth, but at the scale of its size.

Propagation of seismic waves through the heart of Mars

The InSight lander seismometer, photographed by the lander camera on September 23, 2020. NASA/JPL-Caltech

InSight, NASA’s robotic science station, which cost $ 828 million (about $ 704 million), landed on Mars in November 2018. Since then, the lander has used its seismometers – which detect and record earthquakes – to listen to similar earthquakes on Mars. Seismic waves from 12 of these Martian tremors, which traverse the middle of the planet and bounce off the layers within, helped Brigitte Knapmeyer-Endrun’s group map the boundaries of the crust and core.

“Imagine you have a closed box and you want to know what’s inside,” Brigitte Knapmeyer-Endrun imaged. “This method is like taking that box and putting it in an x-ray machine.”

The core of Mars is bigger than scientists thought

Artist’s impression of the Martian core. C. Bickel/Science

Its radius of around 1,839 km was “larger than expected,” Amir Khan, a seismologist at ETH Zurich in Switzerland and co-author of the study, told Insider. The boundary of Earth’s liquid outer core – which surrounds a solid metallic inner core – begins deeper than that of Mars, at about 2,900 km. That said, the Earth is almost twice as wide as Mars, and its core is about twice as wide as well.

Unlike the Earth’s core which is dominated by nickel and iron, the less dense core of Mars contains lighter elements like hydrogen and oxygen. The red planet appears to have no inner core, according to Simon Stähler, another study co-author and Khan’s colleague at ETH. “We don’t know, we’re going to find out,” Simon Stähler told Insider, adding that “the temperatures are probably too high for an inner core to form.”

A more engorged core also means that Mars’ mantle is relatively thinner compared to Earth. It is also devoid of a dense layer of the mineral called bridgmanite which keeps the earth’s mantle stable under high pressure, which could explain the unexpected size of the core. Mineralogically speaking, the mantle of Mars is a “simpler” version of that of Earth, “Amir Khan said.

Mars had, and lost, its protective magnetic field

Visualization of the Earth’s magnetic field. NASA Goddard Space Flight Center

The Earth’s core plays a vital role in protecting the planet from dangerous winds and solar radiation. The liquid iron swirling in the outer core generates a magnetic field that extends from there to the space surrounding our planet.

This vortex is due, in part, to a process in which the warmer, lighter material of the outer core rises into the mantle above. There it is replaced by the cooler, denser mantle matter, which sinks into the lower core. This phenomenon is known as convection. Although Mars has a liquid core, it does not have this swirling motor, known as a dynamo.

Artist’s impression of the different layers of the earth. Getty

Fragments of magnetized Martian crust suggest that the planet once had a magnetic field 4 to 4.5 billion years ago. The absence of the bridgmanite layer in the mantle of Mars could explain why its dynamo stopped about 300,000 years after the formation of the planet. Without this layer, the interior of Mars lost its heat much faster, which paralyzed the convection that was occurring there. In addition, “Mars is smaller and therefore cools faster than Earth,” said Simon Stähler. “Different planet, different story”.

The crust of the red planet is as thick as that of Earth

This illustration shows the NASA InSight spacecraft with its instruments deployed on the Martian surface. NASA/JPL-Caltech

The crusts of the two planets are of similar thickness, according to Brigitte Knapmeyer-Endrun, although the crust of Mars has two or three layers. The average thickness of the Martian crust is between 22 and 71 km. The thickness of the Earth’s crust varies enormously – under oceans it can be as thin as 4.8 km – but under continents it is between 29 and 71 km thick.

But the crust of Mars is very old and static compared to that of Earth, she said. The envelope of our planet is fragmented into tectonic plates that surf the mantle. Through convection, these plates sometimes collide or sink into each other, meaning new pieces of crust are constantly emerging.

Mars lacks this plate tectonics, so no new crust has been generated since the planet’s crust formed around 4.5 billion years ago. The planet was once “probably completely molten” and this hot liquid mass then differentiated into a crust, mantle and core, Khan said.

The lack of plate tectonics is linked, in part, to the slowness of convection in the mantle, according to Simon Stähler. Lack of water also plays a role. “Water lubricates the movement of the plates on Earth,” Stähler explained. “On Mars, the water was probably lost very early on, after the dynamo was gone and the atmosphere was blown away by the solar wind.”

The next target of InSight? The moon

The Moon under the magnifying glass of Mariner 10, in 1973. NASA/JPL/Northwestern University

Scientists had previously used observing the mass, diameter and rotation of Mars from space to predict what its inner layers might look like. Simon Stähler was delighted that InSight’s results match previous predictions. “We were able to confirm very rough estimates made from orbit. So now we know how much we can trust the estimates of the internal structure of Venus or Mercury,” he said.

InSight’s mission to the Red Planet is expected to last until the end of 2022, but scientific explorations of the lander won’t stop next year. InSight will travel to the moon as part of NASA’s Commercial Lunar Payload Services program in 2024, Stähler said.

Version originale : Aylin Woodward/Insider

Read also – NASA’s InSight lander reveals Mars would be much more fragile than we thought