Since last summer, Jupiter’s third-largest moon, Io, has been illuminating the Jovian system with a huge burst of volcanic activity. As the most volcanically active world in the solar system, Io is no stranger to such eruptions, but this year’s show was extraordinarily active.
Researcher Jeff Morgenthaler, who has been monitoring volcanic activity on Io since 2017, says this is the largest eruption he has seen so far. Morgenthaler observations are taken with the Planetary Science Institute’s small-scale Io Input/Output (IoIO) Observatory.
Io experiences phases of volcanic activity on an almost annual basis. The eccentricity of its orbit and its close proximity to Jupiter’s strong gravity cause the Moon to continually bulge and compress, adding energy to the world in a process known as tidal heating. This same process is responsible for the liquid subterranean oceans within nearby moon Europa–but Io is closer to its planet and has a more rocky composition, leading to vast pyroclastic flows, volcanic eruptions, and violent upheavals of the crust.
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These extreme volcanic conditions affect more than just the lunar surface. Io’s surface gravity is low enough (only slightly stronger than gravity on Earth’s moon) that some of the gases and light matter from Io’s volcanoes can escape into orbit around Jupiter. This material consists largely of ionized sulfur, and forms a donut-shaped ring around Jupiter known as an Io plasma torus.
Usually, the torus lights up at the same time that Io is experiencing volcanic eruptions. However, this was not the case with the volcano’s most recent eruption, which lasted from September to December 2022.
Morgenthaler suggests two possible explanations:
“This might tell us something about the composition of the volcanic activity that caused the eruption or it might tell us that the torus is more efficient at ridding itself of material when more material is thrown into it.”
In order to know for sure, we need measurements of the area at the site. Fortunately, NASA’s Juno probe passed through the region in mid-December, coming within 64,000 km of Io on December 14. Juno has instruments on board capable of characterizing the radiation environment inside the torus, and Morgenthaler hopes the data from the flyby will reveal whether there is something different about the formation of this explosion compared to previous ones. Juno Io flyby data is still being downloaded and processed.
Juno is expected to pass near Io next December, coming within 1,500 km of the moon, and it was the closest spacecraft to Io since the Galileo mission in 2002.
Morgenthaler will watch Io and his plasma ring with IoIO after that as well, as long as cloudy weather doesn’t get in the way.
IoIO is a small telescope, and from Earth, it can only see the torus by filtering out light from Jupiter, which is bright enough that it would normally drown out the relatively dim torus. The IoIO uses a coronal vertebra to make sure the telescope is not blinded by the gas giant’s glow.
“One of the exciting things about these observations is that they can be reproduced by almost any junior college or aspiring amateur astronomer,” says Morgenthaler. “Almost all of the parts used to build the IoIO are available at a high-end camera or telescope store.”
IoIO consists of a 35 cm (14 in) Celestron Schmidt-Cassegrain telescope, modified with a custom coronagraph.
“PSI’s Io Input/Output Observatory detects a large volcanic eruption on Jupiter’s moon Io.” Planetary Science Institute.
Featured image: IoIO image of sodium nebula Io in an outburst. Credit: Jeff Morgenthaler, PSI.