Io’s volcanoes have been erupting for billions of years

EarthSky’s Deborah Byrd created this 1-minute video summary for you, on Io‘s volcanoes.

  • Jupiter’s rocky moon Io is the most volcanically active world in the solar system. It has hundreds of volcanoes, some with erupting lava fountains dozens of miles (kilometers) high.
  • Io’s volcanoes have been active for billions of years, a new study says, ever since Io first formed.
  • How do they know? The researchers studied the ratio of different light and heavy sulfur isotopes in Io’s thin atmosphere. The results suggest the volcanoes’ age, and also provide clues about how much sulfur Io has lost since its formation.

Jupiter’s moon Io is famous for the hundreds of volcanoes dotting its surface. It’s the most volcanically active world in our solar system. But how long has Io had its active volcanoes? Researchers at the California Institute of Technology (Caltech), New York University and NASA’s Goddard Space Flight Center said on April 18, 2024, that Io’s volcanoes have been erupting for billions of years, since just after the little moon 1st formed, along with our sun, Jupiter, Earth and the rest of our solar system.

The conclusions are based on new analysis of sulfur in Io’s thin atmosphere. That makes sense, because sulfur plays a key role on Io’s surface and in its atmosphere. Some of Io’s volcanoes spew sulfur and sulfur dioxide in great plumes extending miles (kilometers) above Io’s surface. Extensive plains of sulfur lie in a frosty coating on most of Io’s surface.

If you could stand on Io without a spacesuit (not literally possible since Io is bathed in extreme radiation from Jupiter), you’d find it smells like rotten eggs, due to its sulfur. Now that sulfur has provided clues to the history of Io’s active volcanoes.

The researchers published their peer-reviewed findings in two new papers on April 18, one in Science and the other in JGR Planets.

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Io's volcanoes: Brownish, mottled and patchy planet-like body on black background.
View larger. | NASA’s Juno spacecraft captured this detailed view of Jupiter’s moon Io on October 15, 2023. Io’s volcanoes were the focus of a new study, which concludes they are billions of years old, originating from a time when the moon first formed. Image via NASA/ JPL-Caltech/ SwRI/ MSSS/ Ted Stryk.

New analysis of sulfur isotopes from Io’s volcanoes

So, Io’s volcanoes emit a lot of sulfur. And Io’s atmosphere is 90% sulfur dioxide. The research team conducted an analysis of isotopes of Io’s atmospheric sulfur. This provided clues as to how long Io has been in orbital Laplace resonance with two other moons: Europa and Ganymede.

In other words, Io completes four orbits of Jupiter for every two orbits of Europa and one orbit of Ganymede. As a result, the moons all pull on each other gravitationally. This causes their orbits to be elliptical rather than circular. And in turn, Jupiter’s strong gravity then heats the interiors of the moons. This is why Europa and Ganymede have subsurface oceans and Io has magma and volcanism.

By analyzing the isotopes, scientists could tell how long Io has been in orbital resonance and, therefore, volcanically active. To do this, they used the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.

The sulfur atoms on Io have various isotopes. That is, they have varying numbers of neutrons. Sulfur-32 and sulfur-34 both have 16 protons, but the first has 16 neutrons, while the second has 18. The more neutrons an atom has, the heavier it is. On Io, the heaviest sulfur atoms are at the bottom of the atmosphere, while the lightest are near the top.

Ever-changing surface and atmosphere

Even though Io overall is billions of years old, just like all the other bodies in the solar system, its surface is only about a million years old. This is because its surface is always being replenished by new material from its numerous volcanoes.

Io’s atmosphere is always changing, too. Collisions with charged particles in Jupiter’s magnetic field strip away the already-thin atmosphere into space. This happens at a rate of one ton per second. Therefore, the lighter sulfur isotope at the top of the atmosphere, sulfur-32, gets depleted faster. By calculating how much sulfur-32 is missing, the researchers can determine how long Io has been volcanically active.

This animation is an artist’s concept of Loki Patera, a lava lake on Io, made by using data from the JunoCam imager onboard NASA’s Juno spacecraft. With multiple islands in its interior, Loki is a depression filled with magma and rimmed with molten lava. Video via NASA/ JPL-Caltech/ SwRI/ MSSS/ YouTube.

Sulfur ratios

The researchers looked at the ratio of sulfur-32 to sulfur-34 in Io’s atmosphere. In the early solar system, the ratio was about 23 atoms of sulfur-32 for every one atom of sulfur-34. That ratio is the same today for any body that has remained unchanged since it first formed. But that’s not the case with Io. By far, most of its original sulfur – 92 to 99% – has been lost. Even though so much of the original sulfur – the lighter isotope sulfur-32 in particular – has been lost, this also shows Io must have been volcanically active since soon after its formation.

And that, in turn, shows Io has been in a Laplace orbital resonance with Europa and Ganymede for just as long.

Diagram of Io atmosphere. Circles with smaller circles inside them representing types of gases, with labels.
View larger. | Conceptual model of the sulfur cycle on Io. Image via Hughes et al./ JGR Planets (CC BY 4.0).

History of Io’s volcanoes

While the new findings show Io has always been volcanically active, there are still various possible specific scenarios for the history of the moon. This includes the possibility that Io was once even more volcanically active early on than it is now. As Ery Hughes, formerly from Caltech and co-author of the first paper in Science, explained:

Because lots of the light sulfur is missing, the atmosphere we measure today is relatively ‘heavy’ in terms of sulfur. Key to achieving such heavy sulfur in Io’s atmosphere is the process of burying the heavy sulfur back into Io’s interior, so that it can be released by volcanoes over and over again. Our modeling shows that sulfur gets trapped in the crust of Io by reactions between the sulfur-rich frosts, which are deposited from the atmosphere and the magma itself, allowing it to be eventually buried into Io’s interior.

On April 18, 2024, NASA also released new video animations of a lava lake and steeple-like mountain on Io. Check them out!

Bottom line: A new study reveals Io’s volcanoes have been erupting for billions of years, ever since the small moon of Jupiter first formed.

Source: Isotopic evidence of long-lived volcanism on Io

Source: Using Io’s Sulfur Isotope Cycle to Understand the History of Tidal Heating

Via Caltech

Read more: Jupiter’s moon Io as you’ve never seen it

Read more: Jupiter’s moon Io: Global magma ocean, or hot metal core?

April 24, 2024

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