Tidal heating is a process in which the gravitational pull of a planet or satellite on an orbiting body causes friction and generate heat. The tidal heating of a body is proportional to the product of its mass, eccentricity, and mean motion.
The largest source of tidal energy in the solar system comes from Jupiter’s satellites Io and Europa. Io is heated by tides raised by Jupiter itself and by the other Galilean satellites. The amount of heat generated within Io due to these tidal forces is sufficient to maintain its surface temperature at around 130 K (−143 °C; −225 °F), despite being so close to Jupiter that it has no atmosphere to retain heat. Europa’s much weaker interaction with Jupiter produces only about 1/4 as much heat as Io receives from Jupiter, but this is still enough to maintain a liquid water ocean beneath Europa’s icy crust.
Other moons in the solar system are also tidally heated, though not to the same extent as Io and Europa. Tidal heating plays an important role in the geology of Saturn’s moon Enceladus, where it has resulted in the formation of active geysers spewing water vapor and ice particles into space from fractures near the south pole known as “tiger stripes”. Tidal heating may also be responsible for volcanic activity on Neptune’s moon Triton.