The tidal bore in the Bay of Fundy carries billions of tons of water up the estuary at 15 km per hour, illustrating the immense power of tides. But tidal interactions in planetary systems can do more than produce killer rafting: the Earth’s tidal grip has shaped the Moon’s rotation and orbit over billions of years. But tides also power volcanoes on Jupiter’s moon Io so potent they can be seen across the Solar System and may even be the key to life in the icy moon Europa.