Surprise! The first look at Mars reveals a crust with cake-like layers

The Mars InSight Lander is equipped with a curved seismometer (left) and a probe for measuring the heat flow (right).Photo credit: NASA / JPL-Caltech

NASA’s InSight mission finally took a look inside Mars – and discovered that the planet’s crust could consist of three layers. This is the first time scientists have directly studied the interior of a planet other than Earth, helping researchers figure out how Mars formed and evolved over time.

Before this mission, researchers had only measured the internal structures of the earth and moon. “This information was previously missing on Mars,” said Brigitte Knapmeyer-Endrun, seismologist at the University of Cologne, in a recorded lecture given at the virtual meeting of the American Geophysical Union on December 15th. She declined an interview with natureand says the work is being considered for publication in a peer-reviewed journal.

This is an important finding for InSight, which landed on Mars in November 2018 to determine the internal structure of the planet1. Crouching near the Martian equator on a smooth plain known as the Elysium Planitia, the InSight lander uses an extremely sensitive seismometer to hear the geological energy booming through the planet2. To date, the mission has detected more than 480 “marsquakes,” says Bruce Banerdt, the mission’s lead researcher and scientist at the Jet Propulsion Laboratory in Pasadena, California. Mars is less seismically active than Earth, but more than the moon.

Just as with earthquakes, seismologists use marsquakes to map the internal structure of the red planet. Seismic energy travels through the ground in two types of waves. By measuring the differences in the motion of these waves, researchers can calculate where the core, mantle and crust of the planet begin and end, and how each wave is composed. These basic geological layers show how the planet cooled and formed billions of years ago during the fiery birth of the solar system. “We now have enough data to answer some of these big questions,” says Banerdt.

The continental crust is generally divided into sub-layers of different types of rock. Researchers suspected but didn’t know exactly whether the Martian crust was also stratified, says Justin Filiberto, a planetary geologist at the Lunar and Planetary Institute in Houston, Texas. InSight’s data now shows that it has either two or three layers.

A three-layer crust is best suited to geochemical models3 and studies on Martian meteorites, says Julia Semprich, a planetary scientist at the Open University in Milton Keynes, UK.

Depending on whether the crust actually has two or three layers, it is either 20 or 37 kilometers thick, said Knapmeyer-Endrun during her lecture. That thickness will likely vary in different places on the planet, but it shouldn’t average more than 70 kilometers, she added. On Earth, the crust thickness varies between 5 and 10 kilometers under the oceans and between 40 and 50 kilometers under the continents.

In the coming months, InSight scientists plan to report measurements taken even deeper into Mars, Banerdt says – and will eventually reveal information about the planet’s core and mantle.

In addition to hearing Marsquakes, InSight’s other major scientific goal is to measure the flow of heat through the Martian soil with a probe called a mole. It was supposed to be buried deep in the ground, but made an effort – at some point even jumped out of the ground entirely. The mole has finally managed to dig itself several inches deep, says Banerdt, and will try to dig one last time in the coming weeks before giving up. “We are now at what we think is the final,” he said.