Data taken from Nasa’s Insight lander (pictured) has shown that Mars’ liquid iron core is smaller and denser than previously thought.
A pair of quakes in 2021 sent seismic waves deep into the Red Planet’s core that were captured by Insight, giving scientists the best data yet on its size and composition.
Insight was retired in December 2022 after it stopped responding to communications from Earth, following months of declining power due to Martian dust building up on its solar panels.
Scientists are still poring over the trove of data from its seismometer that were collected over its four years in operation.
The two quakes were the first identified by the InSight team to have originated on the opposite side of the planet from the lander – so-called ‘farside quakes’. The distance proved crucial as the farther a quake happens from InSight, the deeper into the planet its seismic waves can travel before being detected.
The findings mark the first direct observations ever made of another planet’s core.
“We needed both luck and skill to find, and then use, these quakes,” said lead author Jessica Irving, from the University of Bristol. “Farside quakes are intrinsically harder to detect because a great deal of energy is lost or diverted away as seismic waves travel through the planet.”
The two quakes occurred after the mission had been operating on the Red Planet for well over a full Martian year (about two Earth years), meaning the Marsquake Service – the scientists who initially scrutinise seismographs – had already honed their skills.
It also helped that a meteoroid impact caused one of the two quakes; impacts provide a precise location and more accurate data for a seismologist to work with. As Mars has no tectonic plates, most Marsquakes are caused by faults, or rock fractures, that form in the planet’s crust due to heat and stress.
“These two farside quakes were among the larger ones heard by InSight,” said Bruce Banerdt, InSight’s principal investigator. “If they hadn’t been so big, we couldn’t have detected them.”
One of the challenges in detecting these particular quakes was that they’re in a ‘shadow zone’ – a part of the planet from which seismic waves tend to be refracted away from InSight, making it hard for a quake’s echo to reach the lander unless it is very large.
“It took a lot of seismological expertise from across the InSight team to tease the signals out from the complex seismograms recorded by the lander,” Irving said.
Detecting seismic waves that travelled through the core allowed scientists to refine their models of what the core looks like. Based on the findings documented in the new paper, about one-fifth of Mars’ core is composed of elements such as sulphur, oxygen, carbon and hydrogen.
“Determining the amount of these elements in a planetary core is important for understanding the conditions in our solar system when planets were forming and how these conditions affected the planets that formed,” said one of the paper’s co-authors, Doyeon Kim of ETH Zurich.
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