NASA's Juno spacecraft, built with titanium shielding to survive Jupiter's radiation belts, spends its orbits sending back data on what lies beneath the planet's clouds. This Horizon episode follows the mission team as they use Juno's instruments to probe the atmosphere and interior, testing the long-standing theory of a vast ocean of liquid metallic hydrogen churning beneath the surface and generating the planet's magnetic field, the strongest of any planet in the solar system. Scientists explain how Juno's readings are forcing revisions to models of Jupiter's core, and cameras capture the aurorae at the poles, driven by that same magnetism. The film moves between mission control footage, spacecraft imagery, and interviews with the physicists and planetary scientists interpreting the readings, building a picture of Jupiter less as a simple gas ball and more as a layered, violent world with weather systems and magnetic forces far beyond anything on Earth. It closes with what Juno's findings mean for understanding how gas giants form.