Io, one of Jupiter’s moons, has been a hotbed of volcanic activity for billions of years.

Jupiter’s moon Io has been continually modified by volcanic eruptions over billions of years, probably since it first formed.

Io is the most volcanically active object in the solar system, with many volcanoes spewing plumes of sulfurous material that can be seen from Earth. Astronomers now know this is caused by so-called tidal heating, in which the gravity of Jupiter and its nearby moons deforms Io, but they wonder if it’s always been this way or if there was a more benign past. It was unclear whether it was there or not.

now, Catherine de Clear Caltech researchers have discovered that Io has probably been spewing lava for almost the entirety of its history. They did this by measuring the ratio of her two isotopes of sulfur in the atmosphere.

The most common stable form of sulfur contains 16 protons and 16 neutrons in each atom, but a heavier stable form called sulfur-34 has two extra neutrons. On Io, volcanoes continually spew both isotopes into the atmosphere and onto the ground. The top layer of the atmosphere, rich in lighter sulfur atoms, is lost to space as the moon moves around Jupiter, changing the ratio of these isotopes.

De Kleer and colleagues used observations from the Atacama Large Millimeter/submillimeter Array (ALMA), a series of radio telescopes in Chile, to measure the proportions of Io’s atmosphere. Then, by modeling how much sulfur Io loses each year, the researchers were able to see at what point Io’s sulfur ratios are similar to the rest of the solar system. Although it is not possible to say exactly how long the volcano has been active, it appears that it has been erupting for between 2.5 billion and 4 billion years.

Because Io’s volcanic activity is due to tidal heating by Jupiter and other moons such as Europa and Ganymede, the results can also be used to infer the configuration of the Jupiter system billions of years ago. “The length of Io’s volcanic activity is a direct reflection of how long this orbital structure has existed,” de Clare says.

If Io has been consistently volcanically active for billions of years, this also means that its deep geological formations have been recycled many times, they say. Lionel Wilson At Lancaster University, UK.

Sampling the ejected material will provide a rare opportunity to learn about the chemical composition of Io’s deeper layers, such as the mantle beneath its outer shell. “If these volcanoes have continued to erupt essentially throughout the history of the solar system, even if we look at the composition of what’s erupting and find that it’s actually a snapshot of Io’s entire mantle, It’s safe,” Wilson said.