Extract from ABC News
Standing up straight would be a challenge on the Red Planet, with marsquakes rumbling below the surface several times a day.
But for researchers working on NASA's InSight mission, these seismic vibrations offer tantalising clues about what Mars looks like on the inside.
Key points:
- NASA's InSight team has used marsquake data to map the Red Planet's interior
- The planet has a huge liquid core and relatively thin mantle and crust
- The findings challenge previous ideas about what lies beneath the planet's surface
Using data collated over several years, researchers have mapped the planet's crust, mantle and core for the first time — and they look quite different to Earth's interior, according to three studies published today in Science.
Unlike Earth, Mars' liquid core takes up nearly half of its interior, leaving little room for the planet's upper layers.
The findings challenge previous ideas about what lies beneath the planet's surface, according to Suzanne Smrekar, study coauthor and the mission's deputy principal investigator from NASA's Jet Propulsion Laboratory.
Getting to know Mars from the inside
The InSight lander touched down on Mars at the end of 2018 on a volcanic plain known as Elysium Planitia.
While
other Mars missions have focused on finding out what's happening on the
planet's surface, InSight's goal is to work out what lies beneath.
In February 2020, InSight's seismometer picked up 174 marsquakes — vibrations that travel below the surface, similar to earthquakes on our own planet.
Studying how these internal wobbles travel can offer clues about the planet's inner structure, right down the to its liquid core, said Katarina Miljkovic, a planetary scientist at Curtin University who is also involved in NASA's InSight mission.
"These marsquakes can tell us about what the interior structure actually looks like," said Dr Miljkovic, who was not involved in the three new studies.
Mars has a gargantuan liquid core …
NASA's InSight researchers analysed marsquake data collected by InSight's seismometer in 2019.
When they studied faint marsquake signals that had bounced off the planet's core, they discovered that it had a radius of 1,830 kilometres.
The huge liquid core takes up nearly half of the planet's interior.
It's also a melting pot of iron, nickel, and light elements like sulphur, making it less dense than the team expected.
The core's massive size suggests the planet's mantle — the layer that sits between the core and crust — is relatively thin and is made up of just one rocky layer rather than two, like Earth's.
This finding throws water on the idea that there was a layer at the base of the mantle that pushes hot molten rock to the surface, which was once thought to be the driving force behind Mars' huge volcanoes.
"That idea is out the door," Dr Smrekar said.
Using data from eight marsquakes, the researchers were able dive 800 kilometres below the surface for a closer look at Mars' mantle.
They hit upon a thick rocky layer lying almost 500 kilometres deep and found that seismic waves associated with marsquakes slow down as they travel through this mantle layer.
Mars' mantle also lacked a mineral found in Earth's called bridgmanite, which has an insulating effect.
This suggests that Mars' core might have cooled more rapidly in its early days than Earth's did.
… and a surprisingly thin crust
The team were also able to measure the Red Planet's crust — its outermost layer.
Across the planet, Mars' crust is about 24 to 72 kilometres thick on average — slightly thinner than previous estimates, which which fell somewhere between 33 and 81 kilometres.
For perspective, Earth's crust is around 15 to 20 kilometres thick.
"Most estimates of the crustal thickness have been larger than the value that we're finding," Dr Smrekar said.
They also found that Mars' crust is made up of two or possibly even three distinct layers, indicating that it could be made up of different types of rock rather than just one, as previously thought.
Another surprise was that the crust was rich in radioactive elements like uranium and thorium that heat up the planet's outer shell.
"This thinner crust is at the edge of what we thought was possible in terms of the concentrations of these elements," Dr Smrekar said.
"We're going to have to go back and rethink how those elements get concentrated into the crust that formed initially."
Findings bring 'precision' to interior layers
Dr Miljkovic said that the new findings were crucial in building a more accurate picture of the Red Planet's insides.
"It's telling the story about the planet's structure that we really didn't know much about in the past," Dr Miljkovic said.
"We had some idea of how thick the crust was and that there was a core. But [the findings] put a little bit more precision to where the layers are in the interior."
Dr Smrekar said the new results indicate there is still so much to learn about how Mars became the planet is today.
"We have to train ourselves to recognise all these different signatures in seismic waves" she said.
"All these things help us gain new information about the variability inside the planet."
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