Mars InSight Lander Offers a Sneak Peek at the Red Planet’s Inner Layers

The robotic explorer was sent to Mars to study its formation—and the data is now making its way back to Earth

An artist's rendering of InSight. It looks like the robot is sitting atop a piece of land that has been sliced to look like a corner, revealing the layers underneath the surface. The background depicts Mars' red, rocky surface before a yellow sky.
InSight was sent on a mission to answer questions about the Red Planet's crust, mantle and core, known as the "inner space." IPGP/Nicolas Sarter

In November 2018, NASA's robotic explorer InSight landed on Mars' rocky, dusty, red surface. It was sent on a mission to answer questions about the Red Planet's crust, mantle and core, known as the "inner space." The robot is souped up with cutting-edge technology to measure the conditions on the surface and take a look at what's happening beneath the crust, according to NASA.

In a recent finding, researchers announced that Mars' crust looks like it has three layers. This is the first time that scientists have taken an inside look at another planet besides Earth, and the discovery sheds light on how these rocky planets may have formed billions of years ago, reports Alexandra Witze for Nature.

Just like geologists do on Earth, the team used seismometers—instruments used to detect vibrations that ricochet through the crust—to measure what was happening on Mars. Recording how the seismic waves move through the planets' layers could reveal when each layer starts and ends, as well as what they're made out of, Nature reports.

During the meeting, the team also reported that InSight has detected nearly 500 small "marsquakes," but very few with a magnitude greater than 4.5, reports Paul Voosen for Science. Larger quakes send deeper rumbles through the planet's core and mantle, which would allow the team to pinpoint where the quakes originated, but Mars has been "curiously silent," reports Science.

Despite the lack of large marsquakes, the researchers were able to estimate how thick Mars' crust is. They predict it has three layers—but possibly two—that are between 12.4 and 23 miles thick, reports Nature. Mars' crust is considerably thinner than that of Earth, which can be up to 25 miles thick—and that's surprising, reports Science.

An illustration of Mars. The planet looks like it was cut in half and separated. The outside of the sphere is mottled red and brown, and the cross-section reveals a glowing core surrounded by a yellow-orange mantle, then a gray crust.
The researchers predict that Mars' crust is either 12.4 or 23 miles thick, making it considerably thinner than that of Earth, which can be up to 25 miles thick. NASA/JPL-Caltech

Scientists originally theorized that since Mars has less internal heat than Earth, it would have a thicker crust. Mars is still dotted with volcanoes that are no longer active, but ages ago, the volcanoes allowed the hot magma from the planet's insides to bubble up to the surface and build up the crust. However, this discovery throws a wrench in that theory. Since the crust is so thin, it looks like Mars is recycling the older material at the bottom of the crust instead of just piling more material on the top, Stephen Mojzsis, a planetary scientist at the University of Colorado, Boulder who is unaffiliated with the mission, tells Science.

Only around 40 percent of robots sent to Mars have successfully landed, according to NASA. Because of Mars' thin atmosphere, there isn't enough friction to help slow down an incoming spacecraft. But InSight managed to make it there and collect data, and it's providing scientists with invaluable information about the inner workings of the Red Planet. Ultimately, the robot is working to answer some major questions: How did Mars evolve? How did it cool? How did rocky planets form during the birth of the Solar System?

"We have enough data to start answering some of these big questions," Bruce Banerdt, the mission’s principal investigator and a planetary geophysicist at the Jet Propulsion Laboratory in Pasadena, California, tells Nature.

Get the latest stories in your inbox every weekday.