Our knowledge of the Earth’s interior comes from the study of seismic waves during earthquakes, observations of different types of rocks, laboratory experiments, and magnetic and gravitational evidence. But how can we study the interiors of exoplanets, planets orbiting around stars other than our Sun, trillions of kilometers away? About a thousand super-Earths, exoplanets up to twice the size of our planet, have already been discovered with the help of various space and ground-based telescopes. Iron is considered to be...