Jupiter’s moon Io is a dramatic place — even though it’s just 1,131 miles across, or just a bit bigger than Earth’s moon, it hosts over 400 active volcanoes, some of which are as large as 124 miles across. These volcanoes spew out sulfur gases that freeze on the moon’s chilly surface and give it its distinctive yellow and orange color.
Another odd feature about Io is that it has an atmosphere, albeit an extremely thin one. At a billion times thinner than Earth’s atmosphere, it’s barely there, but it does exist and is composed mostly of sulfur from the volcanoes. But researchers weren’t sure about how exactly this atmosphere formed, so recent research has used Earth-based telescopes to examine this puzzle.
“It was not known which process drives the dynamics in Io’s atmosphere,” lead author Imke de Pater of the University of California, Berkeley, explained in a statement. “Is it volcanic activity, or gas that sublimates from the icy surface when Io is in sunlight? What we show is that, actually, volcanoes do have a large impact on the atmosphere.”
The researchers took radio images from the Atacama Large Millimeter/submillimeter Array (ALMA) when Io was moving in and out of the shadow of Jupiter. This change in temperature allowed them to see different states of the sulfur in the atmosphere.
“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,” co-author Statia Luszcz-Cook from Columbia University said. “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 readings showed that between 30% and 50% of the sulfur in the atmosphere comes directly from the volcanoes. And there was an unexpected bonus finding as well: Another gas, potassium chloride, was also spotted coming from the volcanoes. This gas was only spotted in certain regions, suggesting that different magma reservoirs feed different volcanoes on the surface.
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