Researchers are starting to understand Mars’s heart. NASA’s InSight lander has used seismic waves bouncing around the interior of the planet to measure the size of its molten core.
Since landing on Mars in 2018, InSight has measured more than 500 marsquakes, most of them relatively small. When these quakes occur, the lander measures two types of seismic waves – those that skim near the surface and travel in a relatively straight line between the quake and the lander, and those that bounce around within the planet before reaching the detectors. It records the intensity of the waves in a graph called a seismogram.
The InSight team found that many of the records of marsquakes included a set of seismic waves with a shape that suggested they bounced off the boundary between the planet’s mantle and its core. These arrived about 500 seconds after the first surface tremors.
Using that time difference and the direction from which the waves arrived, the team calculated that Mars’s core has a radius of about 1810 to 1860 kilometres, said Simon Stähler at the Swiss Federal Institute of Technology in Zurich, who presented this work on 18 March at the virtual Lunar and Planetary Science Conference.
That size is at the high end of the range of estimates calculated in previous work, which implies that the core may be less dense than we thought, Stähler said. This may mean that Mars’s interior is richer in relatively light elements, such as oxygen, than researchers had realised.
“So far we did not peer into the core itself, but now we know where in the seismogram to look,” said Stähler. “On top of that, we can search for signs of a potential, if unlikely, solid inner core.” However, all the lander’s measurements so far are consistent with the core being entirely molten.
The sensitivity of InSight’s instruments is limited by atmospheric activity on Mars. This means it can detect more marsquakes at night, when the atmosphere isn’t as turbulent, as well as during seasons with fewer dust storms.
Dust storm season at the lander’s location is nearly over, so the InSight team predicts we will see even more marsquakes in the coming months, allowing us to gain a deeper understanding of Mars’s underground structure.
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