'To send a spacecraft there is a little bit insane,' says Scott Bolton when talking about Jupiter, the largest planet in the solar system. But that is exactly what he has done, because Scott is head of Juno, the Nasa mission designed to peer through Jupiter's swirling clouds and reveal the wonders within. But this is no ordinary world. This documentary, narrated by Toby Jones, journeys with the scientists into the heart of a giant. Professor Kaitlin Kratter shows us how extreme Jupiter is. She has come to a quarry to measure out each planet's mass with rocks, starting with the smallest. Mercury is a single kilogram, and the Earth is 17. But Jupiter is on another scale entirely. It is seven tonnes - that is two and a half times the mass of all the other planets combined. On Kaitlin's scale it is not a pile of rocks, it is the truck delivering them. With extreme size comes extreme radiation. Juno is in the most extreme environment Nasa has visited. By projecting a 70-foot-wide, life-siz