Mar’s core roughly half that of Earth’s

Scientists have peered into the heart of Mars for the first time. NASA’s InSight spacecraft, sitting on the Martian surface with the aim of seeing deep inside the planet, has revealed the size of Mars’s core by listening to seismic energy ringing through the planet’s interior, according to a report.

The measurement suggests that the radius of the Martian core is 1,810 to 1,860 kilometres, roughly half that of Earth’s. That’s larger than some previous estimates, meaning the core is less dense than had been predicted. The finding suggests the core must contain lighter elements, such as oxygen, in addition to the iron and sulfur that constitute much of its make-up. InSight scientists reported their measurements in several presentations this week at the virtual Lunar and Planetary Science Conference, based out of Houston, Texas, reported Nature.

Rocky planets such as Earth and Mars are divided into the fundamental layers of crust, mantle and core. Knowing the size of each of those layers is crucial to understanding how the planet formed and evolved. InSight’s measurements will help scientists to determine how Mars’s dense, metal-rich core separated from the overlying rocky mantle as the planet cooled. The core is probably still molten from Mars’s fiery birth, some 4.5 billion years ago.

The only other rocky planetary bodies for which scientists have measured the core are Earth and the Moon. Adding Mars will allow researchers to compare and contrast how the Solar System’s planets evolved. Similar to Earth, Mars once had a strong magnetic field generated by liquid sloshing its core, but that magnetic field dropped dramatically over time, causing Mars’s atmosphere to escape into space and the surface to become cold, barren and much less hospitable to life than Earth’s.

Simon Stähler, a seismologist at the Swiss Federal Institute of Technology in Zurich, reported the core findings in a pre-recorded 18 March presentation for the virtual conference. Stähler declined an interview request from Nature, saying the team intends to submit the work for publication in a peer-reviewed journal.

The work builds on earlier findings from InSight that detected layers in the Martian crust. “Now we start to have that deep structure down to the core,” said geophysicist Philippe Lognonné in another pre-recorded talk. Lognonné, based at the Paris Institute of Earth Physics in France, heads InSight’s seismometer team.

The spacecraft, which cost nearly US$1 billion, landed on Mars in 2018 and is the first mission to study the red planet’s interior. The stationary lander sits near the Martian equator and listens for ‘marsquakes’, the Mars equivalent of earthquakes. So far, InSight has detected around 500 quakes, meaning the planet is less seismically active than Earth but more so than the Moon. Most marsquakes are very small, Lognonné said, but nearly 50 of them have been between magnitude 2 and 4 — strong enough to provide information on the planet’s interior, the report said.