Surprise! A first look inside Mars reveals a crust with cake-like layers

The Mars InSight lander is equipped with a dome seismometer (left) and a probe for measuring heat flow (right).Credit: NASA / JPL-Caltech

NASA’s InSight mission finally looked inside Mars – and discovered that the planet’s crust could be three layers. This is the first time that scientists have researched directly inside a planet other than Earth and will help researchers discover how Mars formed and evolved over time.

Prior to this mission, researchers had measured only the inner structures of the Earth and the Moon. “This information has so far been missing from Mars,” said Brigitte Knapmeyer-Endrun, a seismologist at the University of Cologne in Germany, in a pre-recorded discussion at the December 15 virtual meeting of the American Geophysical Union. She declined an interview with The nature, saying that the paper is being examined for publication in a peer-reviewed journal.

It is a major finding for InSight, which landed on Mars in November 2018, in order to develop the internal structure of the planet.1. The InSight Lander crouched near the Martian equator on a smooth plain known as the Elysium Planitia and uses an extremely sensitive seismometer to listen for geological energy passing through the planet.2. So far, the mission has detected more than 480 “earthquakes,” says Bruce Banerdt, the mission’s lead investigator and scientist at the Jet Propulsion Laboratory in Pasadena, California. Mars is less seismically active than Earth, but more so than the Moon.

As with earthquakes on Earth, seismologists use earthquakes to map the inner structure of the red planet. Seismic energy travels through the ground in two types of waves; by measuring the differences in the way those waves move, researchers can calculate where the core, mantle and crust of the planet and the general structure of each begin and end. These fundamental geological layers reveal how the planet cooled and formed, billions of years ago, at the fiery birth of the solar system. Now, “we have enough data to start answering some of these big questions,” says Banerdt.

The continental crust of the Earth is generally divided into substrates of different types of rocks. Researchers had suspected, but were not sure, whether the Martian crust was stratified, says Justin Filiberto, a planetary geologist at the Lunar and Planetary Institute in Houston, Texas. Now, InSight data shows that it is made up of two or three layers.

A three-layer crust would best suit geochemical models3 and studies of 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 20 or 37 kilometers thick, Knapmeyer-Endrun said during his discussion. This thickness probably varies in different locations on the planet, but is unlikely to exceed an average of 70 kilometers, she added. On Earth, the thickness of the crust varies from about 5 to 10 kilometers below the oceans, to about 40 to 50 kilometers below the continents.

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

Along with listening to earthquakes, InSight’s other great scientific goal is to measure the flow of heat through Martian soil using a probe called a mole. He was meant to bury himself deep in the ground, but he tried to do so – at one point even coming out of the ground. The mole eventually managed to sink a few inches, Banerdt says, and will try to dig one last time in the coming weeks before giving up. “We’re at what we consider to be the final game now,” he says.