A Dozen ‘Marsquakes’ Clue Scientists In to the Red Planet’s Interior

A Dozen ‘Marsquakes’ Clue Scientists In to the Red Planet’s Interior

The first direct seismic observations of Mars by NASA’s InSight Lander have been reported, giving scientists a tantalising look at the composition of the rocky world currently 236 million miles from us.

The observations are detailed in three studies, all published today in Science. The first study explored the thickness and makeup of Mars’ crust; the second study examined InSight data on the upper mantle — the bit just below the planet’s crust; and the third study investigated the Martian core.

All told, the researchers were able to put set ranges on the thickness of each layer of Mars, their densities, and get a gist of interactions between the layers. Perhaps just as importantly, the team’s findings can be compared to Earth’s geoscience, helping the researchers better understand planetary evolution, a major theme of planetary science as space agencies continue to look at the makeup of other bodies in our solar system to better understand our own.

“These three studies provide important constraints on the present-day structure of Mars and are also key for improving our understanding of how the planet formed billions of years ago and evolved through time,” wrote Sanne Cottaar and Paula Koelemeijer, seismologists at the University of Cambridge and Royal Holloway, University of London, respectively, in a Perspectives article on the new information.

Marsquake waves reflected off Mars' interior are received by the InSight lander. (Illustration: Chris Bickel / Science) Marsquake waves reflected off Mars’ interior are received by the InSight lander. (Illustration: Chris Bickel / Science)

InSight landed on Mars in November 2018, charged with measuring the size, range, depth, and structure of the Martian interior. InSight does this by detecting ‘marsquakes,’ which it started doing in early 2019. Marsquakes are a lot like earthquakes, though they occur in stressed portions of Mars’ crust, which doesn’t have tectonic plates like the ones that are associated with earthquakes on Earth.

The InSight teams were specifically looking for shear waves, which are seismic waves that are offshoots of the marsquake event and bounce off different layers of the planet’s interior. Those reflected waves are what InSight is listening for, as they’re bouncing off the hard-to-study layers within Mars. InSight has detected over 1,000 marsquakes so far, but only 12 were of sufficient strength and quality to be studied. None of the 12 registered a magnitude over 4.0.

The first team found the crust was between 15 and 72 km thick, about the thickness of Earth below its continents, and that it was composed of more radioactive, heat-producing elements like thorium and uranium than Earth. In turn, it makes sense that Mars’ surface has more heat escaping from it than Earth, the researchers wrote, and as indicated by the planet’s frigid surface.

Mars’ upper mantle (its lithosphere) was thicker than Earth’s, the second team reported, at around 501 km thick compared to the Earth’s 255-mile-thick mantle. In an email, study author Amir Khan, a geophysicist at ETH Zürich, said that while the planet’s upper mantle mineralogy is similar to that of Earth’s the composition on the two planets is different, indicating that the two planets formed in different fashions.

The planet’s core is larger than previously expected, the third research team reported. It’s mostly molten iron, like Earth’s core. Size of the core aside, the researchers affirmed that the core was liquid. The core results also indicated that Mars’ core would have cooled quicker than Earth’s, potentially creating the geodynamo that sustained a Martian magnetic field for a time. That magnetic field petered out long ago and is now seen in older magnetized rocks on Mars, but the Perspective authors said that the new observations suggest the geodynamo was similar in strength to Earth’s, which is still active today.

“The size of the martian core, the crustal layering, and the thick lithosphere provide important insights into the thermal and dynamic evolution of Mars,” Cottaar and Koelemeijer wrote. “Over the coming years, as more marsquakes are measured, scientists will refine these models of the red planet and reveal more of Mars’ enigmatic mysteries.”

Khan added that InSight’s energy supply remains a concern. The lander has been covered with dust over its tenure on Mars, which has prevented its solar panels from soaking up juice. Though a rather clever stopgap measure was made to slow the lander’s energy depletion, the team will need to figure something out if they want to collect data for years to come. The mission was recently extended through 2022.