Unraveling Io’s Past: Discovering the Moon’s Original Isotope Reservoir Using ALMA and Ancient Meteorites

Io, Jupiter’s moon, is expected to experience modern eruptions that are rich in heavier isotopes of chemical elements due to the escape of lighter isotopes into space over time. By examining the ratios of heavy isotopes to lighter isotopes in Io’s atmosphere, researchers can determine how long it took for the moon to reach its current state from its original underground reservoir of compounds. The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile was used by a team of scientists to observe gases in Io’s atmosphere, specifically sulfur, and estimate 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.