PLANET
How do you study the core of a planet?
Planetary cores, dominated by iron in terrestrial planets, can’t be directly sampled, but geophysics-based methods provide tools to probe the cores of planets and moons. On Earth, seismic waves were used to measure the core’s radius. The nowdefunct InSight mission 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 – in this case marsquakes. 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 or for Mars by orbiters and the InSight lander, 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
