Since last summer, Jupiter’s third largest moon, Io, has been illuminating the Jovian system with a major surge of volcanic activity. As the most volcanically active world in the solar system, Io is no stranger to such outbursts, but this year’s display was exceptionally energetic.
Researcher Jeff Morgenthaler, who has been observing volcanism on Io since 2017, says it is the largest volcanic explosion he has ever seen. Morgenthaler’s observations are taken with the Planetary Science Institute’s small Io Input/Output (IoIO) observatory.
Io goes through phases of volcanic activity almost every year. The eccentricity of its orbit and its proximity to Jupiter’s strong gravity cause the moon to continually inflate and compress, adding energy to the world in a process known as tidal warming. This same process is responsible for the liquid oceans below the surface of neighboring moon Europa – but Io is closer to its home planet and has a rockier composition, leading to major lava flows, eruptions and violent crustal upheavals.
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These extreme volcanic conditions do not just affect the surface of the moon. Io’s surface gravity is weak enough (just slightly stronger than the gravity on Earth’s moon) that some of the gases and light materials from Io’s volcanoes can escape into orbit around Jupiter. Composed largely of ionized sulfur, this material forms a doughnut-shaped ring around Jupiter known as the Io plasma torus.
Usually, the torus clears up as Io experiences a flurry of eruptions. However, that was not the case with the last volcanic outburst, which lasted from September to December 2022.
Morgenthaler offers some possible explanations:
“It could tell us something about the makeup of the volcanic activity that produced the explosion or it could tell us that the torus is more efficient at getting rid of material when more material is thrown into it.”
To be sure, we would need measurements of the region in situ. Fortunately, NASA’s Juno spacecraft passed through the area in mid-December, coming within 64,000 km of Io on December 14. Juno has instruments on board capable of characterizing the radiation environment within the torus, and Morgenthaler hopes data from the flyby will reveal if there was anything different in the makeup of this explosion from previous ones. Juno’s Io hover data is still being downloaded and processed.
Juno is expected to pass even closer to Io next December, less than 1,500 km from the moon, the closest spacecraft to Io since the Galileo mission in 2002.
Morgenthaler will also observe Io and his Plasma Torus with IoIO, 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 to normally drown out the relatively faint torus. IoIO uses a coronagraph to make sure the telescope isn’t blinded by the gas giant’s glow.
“One of the exciting things about these observations is that they can be replicated by almost any small college or ambitious amateur astronomer,” Morgenthaler says. “Almost all of the parts used to build IoIO are available at a high-end camera store or telescope store.”
IoIO consists of a 35 cm (14 inch) Celestron Schmidt-Cassegrain telescope, modified with a custom-made coronagraph.
“PSI’s Io Input/Output Observatory Discovers Large Volcanic Explosion on Jupiter’s Moon Io.” Institute of Planetary Sciences.
Featured Image: IoIO image of the Io Sodium Nebula in an explosion. Credit: Jeff Morgenthaler, PSI.