How do you study the core of a planet?

On Earth, seismic waves were used to measure the core’s radius. The InSight mission has recently used seismic shear waves reflected from the surface of the core to estimate Mars’ core radius. These methods require a lander which is equipped with a sensitive seismometer, and suitable seismic sources. Similar techniques have been used to measure the small lunar core, where both moonquakes and surface impacts were detected. A future seismic mission to the Saturnian moon Titan is planned by NASA.

In the absence of a seismometer, careful estimates of the rotational and gravitational properties of a planet, like those made for Mercury by MESSENGER, can be used to infer properties of the core. Recent observations of vibrations in Saturn’s rings have been used with gravitational measurements to learn about the properties of its huge ice-rock core. Finally, examination of planetary magnetic fields provides important information about the temperature and heat flow inside the cores of some planets within our Solar System.