Scientists have, for the first time, directly measured the core of another planet. NASA's InSight mission on Mars has discovered the Red Planet's core is considerably bigger than expected.


Instruments on the spacecraft have listened to seismic energy deep within the planet. The data suggests a measurement of 1,810-1,860km in diameter, roughly half the size of the Earth's core. It's larger than some predictions, which means the Martian core is less dense than previous estimates, probably due to the presence of lighter elements such as oxygen.

The measurements have not yet been published in a journal but were reported at a virtual gathering of the Lunar and Planetary Science Conference. The finding could help researchers piece together more about how the planet evolved and raises questions about conditions for potential life on the planet.

The measurement was taken with a seismometer, says Divya Persaud, a planetary scientist at UCL, who was not involved in the research.

"It's like a very sensitive ear pressed against the ground, listening for energetic events in the interior of a planet. On Earth, these are usually earthquakes. InSight has detected hundreds of seismic events in the first Martian year of its mission. Seismic events on Mars, like marsquakes or meteorite impacts, are exciting on their own to geologists, but they are also a useful tool.

"On Earth, when an earthquake releases a lot of energy, these waves of energy travel quickly throughout the interior of the planet and bounce off of different materials, like magma, or the boundaries between layers of different types of rock. They also slow down in some materials or speed up in others."

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By measuring the strength of these signals, and how they interact with material underground, scientists can detect the internal structure of the planet. The InSight team used the same technique on Mars.

Persaud is intrigued that the core isn’t as dense as expected, because it may lead to new understandings about how planets and the wider Solar System evolved. "Cores also tell us about energy in the Solar System over time," she says, "not just for Mars but all of the terrestrial planets which formed at the same time but in very different ways from each other.

"Understanding the structure of Mars tells us about how much heat it started with, at what depths, and at what rate through time, and is an important puzzle piece in the bigger mystery of how and why the planets formed the way they did."

InSight, which sits close to the Martian equator, may not be reporting many more findings. Dust is beginning to build up on its solar panels and as Mars moves farther away from the Sun in its orbit, the spacecraft will soon begin to lose its ability to recharge.

However, its discoveries are already game-changing and hint at bigger puzzles to work out. The planet's core might tell us more about an ancient magnetic field that once sustained a Martian atmosphere, not unlike Earth's. This could tell us more about potential life on Mars in the distant past.

"There’s also significance in that InSight has been really successful, technologically," Persaud says. "We only have seismic measurements from the Earth, the Moon, and Mars, and here we have a really successful, advanced instrument that is changing our perspective of Mars. In future, a seismometer on a body like Europa could give us a fantastic look into a radically different world.


"The future of planetary seismology is really exciting."


A former deputy editor at Science Focus, Ian once undertook a scientific ranking of the UK's best rollercoasters on behalf of the magazine. He is now a freelance writer, which is frankly a lot less fun.