Jupiter’s moon Io has been repeatedly remodelled by volcanic eruptions for billions of years, presumably because it first shaped.

Io is essentially the most volcanically energetic physique within the photo voltaic system, spewing plumes of sulphurous materials from its many volcanoes, which might be seen from Earth. Astronomers know that that is at the moment pushed by so-called tidal heating because the gravity of Jupiter and close by moons deforms Io, but it surely was unclear if that was all the time the case or whether or not there had been a calmer previous.

Now, Katherine de Kleer on the California Institute of Expertise and her colleagues have discovered that Io has in all probability been blasting out lava for nearly its whole historical past. They did this by measuring the ratio of two isotopes of sulphur in its ambiance.

Sulphur’s most typical steady kind accommodates 16 protons and 16 neutrons in every atom, however a heavier steady kind known as sulphur-34 has two further neutrons. On Io, volcanoes are consistently spewing each isotopes into its ambiance and onto its floor. The very high layer of its ambiance, which accommodates extra of the lighter sulphur atoms, is misplaced to house because the moon travels round Jupiter, which adjustments the ratio of those isotopes.

De Kleer and her colleagues used observations from the Atacama Giant Millimeter/submillimeter Array (ALMA), a set of radio telescopes in Chile, to measure the ratio in Io’s ambiance. Then, by modelling how a lot sulphur Io may be dropping every year, the staff may work again to seek out out when Io’s sulphur ratio regarded like the remainder of the photo voltaic system. Though they will’t say precisely how lengthy it has been volcanically energetic, it seems to have been erupting for between 2.5 and 4 billion years.

As a result of Io’s volcanism is all the way down to tidal heating by Jupiter and its different moons, like Europa and Ganymede, the outcomes will also be used to deduce the association of the Jovian system billions of years in the past. “Io’s longevity of volcanism immediately displays how lengthy this orbital configuration has been current,” says de Kleer.

If Io has been constantly volcanic for billions of years, then this additionally means it’s going to have recycled its deeper geological layers many occasions over, says Lionel Wilson at Lancaster College within the UK.

This presents a uncommon alternative to seek out out concerning the chemical make-up of Io’s deeper layers, such because the mantle that lies under its outer crust, by sampling the fabric that’s blasting out, he says. “If these volcanoes have been erupting for the entire photo voltaic system historical past, primarily, then it’s secure to have a look at the composition of what’s popping out and know that that’s actually a snapshot of the complete mantle of Io,” says Wilson.