Io’s Eruptions Enriched with Heavier Isotopes: How Scientists Discovered Io’s Evolutionary Past Using Ancient Meteorites and Space Observations

The eruptions on Io are expected to be enriched in heavier isotopes of chemical elements due to the escape of lighter isotopes into space over time. By measuring the ratios of heavy isotopes to lighter isotopes in Io’s atmosphere, researchers can calculate how long it took for Io to reach its current state from its original underground reservoir of compounds. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a team observed gases in Io’s atmosphere, particularly sulfur, and estimated the moon’s original reservoir of isotopes using ancient meteorites.

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.