Cross-section of the Earth (left) and the exoplanet Kepler-138 d (right). Like the Earth, this exoplanet has an interior composed of metals and rocks (brown portion), but Kepler-138 d also has a ...

Cross-section of the Earth's interior: crust, upper- and lower-mantle, and outer- and inner-cores. Credit. Mikio Fukuhara, Alexander Yoshino, and Nobuhisa Fujima. Usage Restrictions.