New Radio Images Show Direct Effect of Volcanic Activity on Io's Atmosphere

A new set of radio images taken by the Atacama Large Millimeter/ submillimeter Array (ALMA) has captured the direct impact of volcanic activity on Io's atmosphere.

For the first time ever, the images in the report show the dynamics occurring in the atmosphere of Jupiter's moon. Io is often notable among the moons in the solar system for its large number of active volcanoes, with previous studies identifying more than 400 of them shooting out sulfur gases. As the satellite with the greatest volcanic activity, the chemicals spewed out from volcanoes freeze above its surface, giving Io its distinct multicolor appearance.

Past works have identified sulfur dioxide gas, also from Io's volcanic activity, as the most abundant chemical in Io's atmosphere. However, Imke de Pater, a member of the ALMA team from the University of California, Berkeley, notes that the processes behind Io's atmosphere remain unknown.

"Is it volcanic activity, or gas that has sublimated (transitioned from solid to gaseous state) from the icy surface when Io is in sunlight?" de Pater inquired.

Capturing Io's "Eclipse"

To understand how volcanic activity interacts with and affects the atmosphere, astronomers used the large radio telescope to take images of Io as it passed through Jupiter's shadow - a term the ALMA team referred to as an "eclipse."

Statia Luszcz-Cook, co-author of the report from Columbia University in New York, explained that when Io passes into the shadow of its planet, the lack of sunlight makes it too cold and condenses sulfur dioxide gas. During that time we can only see volcanically-sourced sulfur dioxide. We can therefore see exactly how much of the atmosphere is impacted by volcanic activity."

The researchers were able to clearly identify the movement of sulfur monoxide (SO) and sulfur dioxide (SO2) plumes moving from volcanoes to the atmosphere. ALMA is equipped with a total of sixty-six antennas that work together to create a large, unified telescope - making these detailed observations on Io possible.

Aside from the sulfur compounds, the ALMA team also identified a third gas spewed by volcanoes: potassium chloride (KCl). "We see KCl in volcanic regions where we do not see SO2 or SO," explained Luszcz-Cook. She also notes that this strongly suggests the presence of different magma reservoirs underneath different volcanoes.

Io's Volcanic Activity

Io's unusual volcanic activity is attributed to a phenomenon called tidal heating. When a moon orbits its planet in an elliptical orbit, the same side of the moon faces the same side of its planet. This can be observed with Jupiter and Io, as well as Earth and the Moon. In Io's case, the gravitational pull of Jupiter's other larger moons, specifically Ganymede and Europa, causes internal friction and heat that creates volcanoes. It includes Io's largest moon, Loki Patera, which extends to 202 kilometers (126 miles) in diameter.

"By studying Io's atmosphere and volcanic activity we learn more about not only the volcanoes themselves, but also the tidal heating process and Io's interior," Luszcz-Cook explained.

Astronomers are looking to understand another of Io's mysteries next: its atmospheric temperature. De Pater notes that to achieve this, they require a higher resolution for their observations. Also, to measure Io's temperature, they would have to monitor Jupiter's moon for a longer time.

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