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Sodium, Not Heat, Reveals Volcanic Activity on Jupiter’s Moon Io


IoIO consists of a 14-inch (35 cm) Celestron Schmidt-Cassegrain telescope feeding a custom-built coronagraph. An Astro-Physics 1100 mount, 80mm offset guide scope, and associated software enable the system to acquire and guide on Solar System targets robotically. The telescope is hosted at the San Pedro Observatory in Benson, Arizona, 40 miles east of Tucson. 

A large volcanic event was detected on Jupiter’s moon Io using Jovian sodium nebula brightness variation, a paper in Astrophysical Journal Letters by PSI Senior Scientist Jeff Mortenthaler says. 

“These results highlight the growing body of evidence that the traditional way of monitoring Io's volcanism – by looking for temperature changes on its surface caused by hot lava – is not able to reliably find these large gas release events,” said Morgenthaler, lead author on the paper “Large Volcanic Event on Io Inferred from Jovian Sodium Nebula Brightening.” PSI Senior Scientist Julie Rathbun is a co-author on the paper. 

“Lack of a strong infrared counterpart to this event tells us something about the geology of Io. To use some well-known Earth analogies, this volcanic event may have been from an eruption more like that of Mount St. Helens in 1980, which released lots of gas and dust, rather than Kilauea’s recent eruptions in Hawaii, which produce lots of hot lava,” Morgenthaler said. 

“The volcanic event occurred sometime between mid-December 2017 and early January 2018. Gas from the event filled Jupiter’s magnetosphere, the region of space dominated by Jupiter’s magnetic field, with excess material until early June,” Morgenthaler said. “Io is the most volcanic body in the solar system, so its volcanism is the ultimate source of the material. Interestingly, this event, which was the longest recorded by this technique, was not independently reported by any other Io volcanic monitoring technique, despite significant number of observations in support of NASA's Juno mission.” 

A small telescope popular with amateur astronomers was used to detect the volcanic event. Planetary Science Institute’s Io Input/Output facility (IoIO), is outfitted with a coronagraph, which reduces the intensity of the light from Jupiter and allows light coming from clouds of gas around Jupiter to be imaged through special filters.

Visit to see a video animation of sodium (left) and ionized sulfur (right) emission around Jupiter (under black strip) recorded by PSI's Io Input/Output facility (IoIO) over a three-month period. The animation shows the dynamic nature of the system: Io orbits Jupiter every 1.5 days and Jupiter rotates every 10 hours. The strong magnetic field of Jupiter traps the ring of sulfur ions, known as the Io plasma torus, shown in the right panel.

The project is funded by a National Science Foundation grant to PSI.

Feb. 17, 2019

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