In a recent study, researchers used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe gases in Io’s atmosphere, particularly sulfur. By analyzing the ratios of heavy isotopes to lighter isotopes in Io’s atmosphere, they were able to estimate the moon’s original reservoir of compounds and calculate how long it took for Io to reach its current state from its original underground reservoir.
The analysis revealed that Io has lost 94 to 99 percent of its original sulfur reservoir, indicating that the moon has been erupting for approximately 4.5 billion years. This finding aligns with existing models of Jupiter’s evolution and the inner moons’ history. Despite the chaotic dynamics of planetary satellites, Io, Ganymede, and Europa have been orbiting in a similar pattern for billions of years. This long history of orbital dance suggests that Io’s current state is representative of its evolution over time.