Mars InSight: mission unveils surprising secrets of red planet's interior – new research - The Conversation AU

The signals used to probe the Martian interior all come from relatively small quakes, the best among the hundreds detected so far.

We expect rocky planets like Mars to have an iron-rich core, followed by a silicate layer called the mantle and an outermost skin known as the crust.

Instead, to estimate its size, we used seismic waves (created by marsquakes).

On Earth, the core’s radius was first estimated by finding its “shadow” – an area where the core disrupts the arrival of seismic waves from distant earthquakes.

Our study had to rely on a particular kind of slow, sideways-travelling waves called S-waves which have been reflected back to the surface by the interface between the core and the mantle.

Combined with information from mineral physics and from seismic waves travelling through the mantle, we were able to estimate the size and density of the Martian core.

In the second new study, another team investigated seismic waves which converted from P-waves, which are rapid, compressional waves, to S-waves (or vice versa) when they encountered different rocky material, and an assessment of background vibrations and gravity, to probe the Martian crust.

From over 100 years of seismology on Earth, we know that beneath the thin crust lies the mantle, but the mantle itself is not uniform all the way to the core.

To sample different depths of the mantle we can use both direct and reflected seismic waves.

Reflected waves return to the surface and then dive again two or three times.

A third study identified eight low-frequency marsquakes that produced both direct and reflected waves, and used these to create and test different models of the Martian crust and mantle.