ALMA Detects Direct Evidence Of Volcanic Activity In Io's Atmosphere

One of the celestial bodies that astronomers and researchers are studying intently is Jupiter's moon Io. New radio images from the Atacama Large Millimeter/submillimeter Array (ALMA) have shown direct evidence of volcanic activity on Io for the first time. The moon has an extremely thin atmosphere, said to be about a billion times thinner than Earth's atmosphere. Despite its extreme thinness, the atmosphere can provide a window into the moon's interior and what's happening below its crust.

Io has more than 400 active volcanoes on its surface that spew sulfur gases giving the moon its yellow-white-orange-red colors when the gas freezes. It's the most volcanically active moon in the solar system. Past research showed the atmosphere of the moon was dominated by sulfur dioxide gas from volcanic activity. Researchers want to know what process drives the dynamics in IO's atmosphere.

Specifically, scientists want to know if the dynamics result from volcanic activity or gas that has transitioned from a solid to a gaseous state when the moon is in sunlight. ALMA made snapshots of Io when it passes in and out of Jupiter's shadow to help distinguish between the different processes that give rise to the moon's atmosphere. When Io is in Jupiter's shadow and out of direct sunlight, it's too cold for sulfur dioxide gas, causing the gas to condense onto the surface.

When the moon is in Jupiter's shadow, we only see sulfur dioxide that comes from volcanic activity. While in the shadow of its planet, we only see sulfur dioxide that results from volcanic activity allowing direct observation of how much of the atmosphere is impacted by those volcanoes.

The high-resolution ALMA offers allowed astronomers, for the first time, to see plumes of sulfur dioxide and sulfur monoxide rising from the volcanoes. Scientists were able to determine that active volcanoes directly produce 30 to 50 percent of Io's atmosphere. ALMA also showed that potassium chloride is emitting from the volcanoes, hinting that magma reservoirs vary under the volcanoes.