Scientists have been curious for years about what is hidden beneath the surface of Mars. With its freezing temperatures, red dust, and dry valleys, the surface of the planet has received most of the attention. But something big is buried deep inside Mars’ mantle.
Thanks to NASA’s Insight lander, we’re finally getting a clearer look below the surface. And what’s there is surprising: leftover chunks from ancient cosmic crashes are buried deep in the planet’s mantle.
These rocky fragments aren’t small. Some are as wide as 2.5 miles (4 kilometers). They’re scattered across Mars’ interior like forgotten debris from the solar system’s wild early days.
Mars got slammed – hard
Giant space rocks – possibly even protoplanets – crashed into Mars some 4.5 billion years ago. They impacted hard enough to melt enormous chunks of the planet’s crust and mantle, and form vast oceans of molten rock.
When those impacts occurred, they shattered the surface. They blasted rocky debris, including parts of the impactors, deep into the interior of the Red Planet.
Unlike Earth, which constantly reshuffles its crust through plate tectonics, Mars’ crust is made of a single plate that has stayed mostly stable.
That’s why those ancient impact scars haven’t been erased. The fragments are still down there, frozen in place like time capsules.
“We’ve never seen the inside of a planet in such fine detail and clarity before,” said Constantinos Charalambous of Imperial College London, the paper’s lead author.
“What we’re seeing is a mantle studded with ancient fragments. Their survival to this day tells us Mars’ mantle has evolved sluggishly over billions of years. On Earth, features like these may well have been largely erased.”
InSight sees into Mars’ mantle
All of this comes from a mission called InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. It was run by NASA’s Jet Propulsion Laboratory in Southern California and the lander arrived on Mars in 2018.
InSight was the first lander to place a seismometer on Mars’ surface. That device was incredibly sensitive and recorded 1,319 marsquakes before the mission ended in 2022.
Quakes send out waves that travel through the planet. As those waves move through different materials, they change speed and direction.
Scientists can study how those waves behave to figure out what’s inside the planet, kind of like how doctors use ultrasound to see inside the human body.
“We knew Mars was a time capsule bearing records of its early formation, but we didn’t anticipate just how clearly we’d be able to see with InSight,” said Tom Pike of Imperial College London, coauthor of the paper.
What causes marsquakes?
Marsquakes still happen, usually for two reasons. Some are caused when rocks crack under pressure and heat. Others are caused by meteoroids slamming into the surface.
A study published earlier this year in Geophysical Research Letters showed that meteoroid impacts can create high-frequency seismic waves.
These waves travel deep into the mantle, which is a thick layer of rock beneath the crust. The mantle can be nearly 960 miles (1,545 kilometers) thick, and reach temperatures as high as 2,732 °F (1,500 °C).
Eight of the marsquakes recorded by InSight had strong, high-frequency signals that got noticeably scrambled and delayed.
“When we first saw this in our quake data, we thought the slowdowns were happening in the Martian crust,” Pike said.
“But then we noticed that the farther seismic waves travel through the mantle, the more these high-frequency signals were being delayed.”
Buried lumps in Mars’ mantle
Computer simulations helped scientists figure it out. Those delays only happened when the quake waves passed through small regions of the mantle that had a different composition from everything around them. These were the buried impact fragments.
Some were massive. Others were smaller. All were mixed into the mantle, which Charalambous compared to “shattered glass – a few large shards with many smaller fragments.”
That fits with what we already know: In the early solar system, planets like Mars got hit often and hard.
Charalambous said the fact that these features are still visible “tells us Mars hasn’t undergone the vigorous churning that would have smoothed out these lumps.”
What other planets might be hiding
This discovery doesn’t just help us understand Mars. It also gives clues about other rocky planets – especially ones that don’t have tectonic activity, like Venus and Mercury.
If Mars is holding onto traces of ancient impacts deep in its mantle, maybe those planets are, too.
Mars has always been a quiet planet on the surface. But now we know that, deep inside, it’s holding the scars of an ancient and violent past – and it hasn’t let them go.
The study was published in the journal Science.
Image credit: NASA/JPL-Caltech
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–