We are happy to share that another robotic explorer, NASA’s Mars InSight, is making headway on one of its key mission goals: mapping the internal structure of Mars. This lander came equipped with a very sensitive seismograph, capable of actually measuring not just the primary shake of a marsquake, but also the echoes as the seismic waves move multiple times through the planet. This extreme sensitivity allows this single seismograph to determine the sources of quakes and use the timing differences in how different kinds of waves travel through the world to map out density variations within Mars. 

New results, published in Geophysical Research Letters, by Sizhuang Deng & Alan Levander, find that Mars has three subsurface boundaries – places where the density of the planet shifts. There is a solid inner core, surrounded by a mantle with two density regions, with a crust floating on top. These three measured layers are consistent with prior models that looked at Mars’ moment of inertia and other factors, and allow scientists to directly measure what previously could only be inferred. They found the mantle is roughly 22 miles (35 kilometers) thick at the lander’s location.

The next transition is harder to explain, and here we quote from the Rice University press release: The second is a transition zone within the mantle where magnesium iron silicates undergo a geochemical change. Above the zone, the elements form a mineral called olivine, and beneath it, heat and pressure compress them into a new mineral called wadsleyite. Known as the olivine-wadsleyite transition, this zone was found 690-727 miles (1,110-1,170 kilometers) beneath InSight.

Finally, the boundary between the mantle and Mars’ iron-rich core appears 945-994 miles (1,520-1,600 kilometers) below the lander.

Mars is a large solid ball of rock – complex layered rock – and thanks to InSight, those complexities have been revealed. Way to go, little robot.

More Information

Rice University press release 

“Autocorrelation Reflectivity of Mars,” Sizhuang Deng & Alan Levander, 2020 Aug. 4, Geophysical Research Letters