How do Jupiter’s moons create tidal heating inside Europa?

Europa’s orbit is slightly elliptical, so the strength of Jupiter’s gravity changes during each lap around the planet. In addition, resonances with Io and Ganymede keep pulling on Europa, preventing its orbit from becoming perfectly circular. This repeated flexing creates frictional heat inside the moon, a process called tidal heating. Scientists think that heat may be enough to maintain a subsurface ocean beneath an ice shell that is probably tens of kilometers thick, making Europa one of the best places to search for conditions suitable for life.