First Observations Of Sulfur Dioxide Plumes Reveal How Volcanoes Impact Io’s Atmosphere

Composite image showing for the first time plumes of sulfur dioxide (in yellow) rise up from its volcanoes. Jupiter is visible in the background (Cassini image). ALMA (ESO/NAOJ/NRAO), I. de Pater et al.; NRAO/AUI NSF, S. Dagnello; NASA/JPL/Space Science Institute

Jupiter’s moon Io is the most volcanically active moon in the Solar System. It has more than 400 active volcanoes spewing sulfur into the thin atmosphere. However, it was unclear if the main process driving the amount of gas in the atmosphere was the volcanoes or sublimation of material from the icy surface into the air. Now, new observations have confirmed for the first time how volcanic eruptions impact the thin layer of air around Io.

In a paper accepted for publication in The Planetary Science Journal, researchers report the first-ever observations of the plumes of sulfur dioxide from Io's volcanoes, which shows the origin of the gas in Io's atmosphere, an atmosphere about a billion times thinner than Earth’s own. 

Sublimation, the turning of a solid into a gas, is driven by sunlight, so the team knew that to confirm or rule out sublimation as the main mechanism they needed to get the Sun out of the equation. They studied Io as it moved into the shadow of Jupiter during an eclipse.

“When Io passes into Jupiter’s shadow, and is out of direct sunlight, it is too cold for sulfur dioxide gas, and it condenses onto Io’s surface. 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,” co-author Statia Luszcz-Cook from Columbia University explained in a statement.

The incredibly clear observations from the Atacama Large Millimeter/submillimeter Array (ALMA) allowed astronomers to see the plumes of sulfur dioxide and sulfur monoxide (In yellow in the video below) rise from the volcanoes. The great resolution showed that 30 to 50 percent of the moon’s atmosphere is directly produced by Io's volcanoes.

The team has shown that with these measurements they can gain insight into not just Io's atmosphere but also the interior processes. The discovery of different gases in different regions of Io suggests that not all magma reservoirs on the moon are the same.

The next step is to measure the temperature of Io's atmosphere, which is not an easy task.

“To measure the temperature of Io’s atmosphere, we need to obtain a higher resolution in our observations, which requires that we observe the moon for a longer period of time. We can only do this when Io is in sunlight since it does not spend much time in eclipse,” said lead author Imke de Pater from the University of California, Berkeley. “During such an observation, Io will rotate by tens of degrees. We will need to apply software that helps us make un-smeared images. We have done this previously with radio images of Jupiter made with ALMA and the Very Large Array (VLA).”

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