The most volcanically active moon of Jupiter is Io. Its surface is constantly reshaped by lava flows, volcanic pits, and towering plumes powered by intense tidal heating.
Io is trapped in a gravitational tug-of-war between Jupiter and the nearby moons Europa and Ganymede. Their orbital resonance keeps Io’s orbit slightly eccentric, so Jupiter’s pull repeatedly stretches and squeezes the moon. The resulting friction heats Io’s interior, driving volcanism far more powerful than anything currently seen on Earth.
Before Voyager 1 reached Jupiter in 1979, scientists expected Io to resemble a geologically quiet moon. Instead, imaging scientist Linda Morabito discovered a volcanic plume in the spacecraft’s photographs. More than 150 active volcanic centers have since been observed, with some eruptions sending sulfur and sulfur dioxide hundreds of kilometers above the surface. Io’s sulfur-rich landscape can change noticeably within only a few years.