Volcanoes have been violently erupting on Jupiter's moon Io ever since it was born

Io, Jupiter's moon and the most volcanic body in the solar system, has been in upheaval for at least 4.57 billion years.

Scientists used the Atacama Large Millimetre/submillimetre Array (ALMA) to track sulphur and chlorine in the Jovian moon's atmosphere. While they knew that the gravitational forces between Jupiter and the neighbouring Jovian moons Europa and Ganymede generate immense tidal forces within Io, causing intense volcanism, they weren't sure about how long the influence of Jupiter and its moons had been causing the disruption. It was tough to investigate as the continuous flow of lava from the extreme volcanism across the surface of Io keeps it looking fresh.

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Katherine de Kleer, team leader and assistant professor of planetary science and astronomy at Caltech, told Space.com, "Io's surface is very 'young,' meaning that the lava flows and volcanic plume deposits cover up any features that are more than around 1 million years old. Therefore, it has not previously been possible to learn anything about Io's volcanic history beyond the past million years, which is very recent from a geological perspective. Io represented a big mystery because its surface doesn't hold a record of its history the way that the surfaces of less active moons do."

Katherine and her colleagues used ALMA, an array of 66 radio antennas in the Atacama Desert of northern Chile, to look for clues in Io's thin atmosphere.

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They specifically searched for stable radio isotopes of sulphur and chlorine-bearing molecules. The researchers found that both elements are more present in heavy isotope variants, atoms with a higher number of neutrons, than the average value found across the solar system that occurs as the result of lighter isotopes from other world's upper atmospheres.

They found that the Jovian moon has lost 94 to 96 per cent of its lighter sulphur isotopes. It would have only been possible in the face of billions of years of volcanism going back to the origin of Io.

"We used sulfur isotopes in Io's atmosphere to deduce that Io has been producing sulphur-rich gas — and, therefore, that it has been volcanically active — for billions of years," de Kleer said. "This is a nice confirmation of some prior predictions that have been made," she added.

While de Kleer's team has found something crucial, they aren't done with Io yet. "As for what is next, I'd love to know whether Io once had a water ocean and ice crust, as its neighbors Europa and Ganymede do, that was subsequently lost by volcanism or some other means," de Kleer concluded.

(With inputs from agencies)