Mars hides a radioactive sea of ​​magma beneath its surface

In 2021, it seems as if Mars has a surprisingly big heart. Scientists have been using InSight, a robotic lander, to study the planet’s interior. The spacecraft heard enough Martian earthquakes to form a picture of the layer cake nature of Mars’ underworld.

The shell and mantle were not particularly strange. However, the core was very large, and not very dense, for such a small planet.

For some researchers, this basic measurement was not valid.

“We missed something,” he said. Amir Khan, a geophysicist at ETH Zurich in Switzerland who studied the InSight data. “but what?”

It turns out that Mars’ core is small, Dr. Khan and other researchers have discovered.

in two studies Researchers re-evaluated InSight’s seismic record, which was published Wednesday in the journal Nature. Both teams independently concluded that the Martian core is more similar to the heavy metal core of our universe than previously thought. The initial estimate of the higher size was the result of an undiscovered ocean of molten rock 90 to 125 miles deep, which made the core appear larger than it actually was.

But the deep magma sea, hidden beneath Mars’ solid mantle, kept molten by radioactive elements, is strange. “It does not exist on Earth,” Dr. Khan said, and its presence may require rethinking the chaotic evolution of the Red Planet.

Scientists have studied the Earth’s geological layers for more than a century using the luminous power of seismic waves generated by an earthquake. The InSight rover, which landed on Mars in November 2018, was sent to see if the world’s rusty innards were similar.

But studying Mars using a single seismometer has proven difficult. InSight’s instruments detected only a few modest earthquakes, which mostly came from… Twitch area Close to the spacecraft, only a small slice of the Martian pie has been seismically imaged. For a time, Martian quakes also seemed to bounce off but not penetrate the planet’s deepest core, revealing precious little information about the core.

The researchers determined that the radius of Mars’ core was about 1,140 miles, suggesting that it was not very dense. The cores of terrestrial planets were supposed to be iron-rich, but this was eventually confirmed in the bulging core of Mars. Completely liquid – It appeared 27 percent lighter than pure liquid iron. The implication was that the Martian core was strangely rich in lighter elements such as sulfur, carbon, oxygen and hydrogen – a hazy substance that should have been blown away by the young sun before Mars formed.

Puzzled, scientists hoped that stronger seismic diffraction would provide clarity. And on September 18, 2021, the sky surrendered: a meteor careened into the hemisphere opposite InSight, releasing seismic waves that blasted through the core and bounced around its edges.

“That was the turning point,” he said. Henry Samuela geophysicist at Paris City University and author of one of the new studies.

Based on a model of the thermal and chemical evolution of Mars, Dr. Samuel and his colleagues proposed the existence of A Interbedded magma ocean core In 2021. But “we don’t have any seismic evidence,” he said. With this meteorite impact, his team confirmed the existence of this ultra-hot radioactive soup.

Dr Khan’s team also took advantage of the effect to re-examine InSight’s seismic data, combining it with computer simulations exploring how iron-rich alloys behave at a molecular level – and in doing so, they independently discovered Mars’ hidden magma ocean.

Its presence means the liquid core has a radius of closer to 1,000 miles, and is a denser, iron-rich celestial body with fewer lighter elements, which is easier to explain.

He said the discovery is “absolutely fascinating,” and the combined conclusions of the studies are compelling Paula Colemier, a seismologist at Oxford University, was not involved in the research. “But they may open up a new problem.”

Before it collapsed 3.8 billion years ago, Mars had a magnetic field protecting its atmosphere. Scientists believed that the magnetic field was generated by cooling the liquid iron core, thus mixing it strongly. But a radioactive blanket of magma would have kept the core very warm.

Therefore, a new origin story for Mars’ magnetic bubble is needed. Dr. Samuels offered one suggestion: Mars may have long ago had moons larger than its current ones, the kind whose strong gravity could set off magnet-making movements in the core. But he said this is just a hypothesis at the moment.

Four years later, InSight died in 2022. But the discovery of this magma ocean probably won’t be the mission’s last surprise. “This is just the beginning,” Dr. Samuel said.