Since last summer, Jupiter’s third largest moon, Io, has been illuminating the Jovian system with a violent 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 unusually energetic.
Researcher Jeff Morgenthaler, who has been monitoring volcanism on Io since 2017, says this is the largest volcanic eruption he’s seen to date. Morgenthaler’s observations were made with the Planetary Science Institute’s small Io Input/Output Observatory (IoIO).
Io goes through phases of volcanic activity almost annually. The eccentricity of its orbit and proximity to Jupiter’s strong gravity causes the moon to continuously bulge and compress, adding energy to the world in a process known as tidal heating. The same process is responsible for the liquid subsurface oceans on nearby moon Europa – but Io is closer to its planet and has a rockier composition, resulting in extensive lava flows, eruptions and violent crustal movement.
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These extreme volcanic conditions don’t just affect the lunar surface. Io’s surface gravity is low enough (just slightly stronger than Earth’s moon’s gravity) that some of the gases and light materials from Io’s volcanoes can escape into orbit around Jupiter. This material is mostly ionized sulfur and forms a donut-shaped ring around Jupiter known as the Io plasma torus.
Io’s plasma torus, composed of ionized sulfur, seen from IoIO. Credit: Jeff Morgenthaler, PSI.
Usually, when Io experiences a burst of eruptions, the torus brightens simultaneously. However, this was not the case with the recent volcanic eruption, which lasted from September to December 2022.
Morgenthaler suggests a few possible explanations:
“This could tell us something about the composition of the volcanic activity that caused the eruption, or it could tell us that the torus is more efficient at clearing itself of material as more material is thrown into it.”
The brightness of the Jupiter Sodium Nebula at three different distances from Jupiter (top) and the Io plasma torus (bottom), showing several modest outbursts since 2017 and a major outburst in fall 2022. Credit: Jeff Morgenthaler, PSI.
To know for sure, we would need on-site measurements of the region. Fortunately, NASA’s Juno probe passed the area in mid-December and came within 40,000 miles of Io on Dec 14. Juno carries instruments capable of characterizing the radiation environment inside the torus, and Morgenthaler hopes the flyby data will show if the composition of this burst differs from previous ones. Juno’s Io flyby data is still being downloaded and processed.
Juno is expected to fly even closer to Io next December, coming within 1,500 km of the Moon, the closest possible to Io since the Galileo mission in 2002.
Image of Io taken on December 14, 2022 by the Juno spacecraft from 64,000 km away: Credit: NASA/JPL-Caltech/SwRI/MSSS.
Even then, Morgenthaler will be observing Io and its plasma torus with IoIO, as long as cloudy weather does not intervene.
IoIO is a small telescope, and from Earth it can only see the torus by filtering out light from Jupiter that is bright enough to normally drown out the comparatively faint torus. IoIO uses a coronagraph to ensure 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 small college or ambitious amateur astronomer,” says Morgenthaler. “Almost all of the parts used to build IoIO are available at a high-end photo store or telescope shop.”
IoIO consists of a 35 cm (14 inch) Celestron Schmidt-Cassegrain telescope modified with a custom built coronagraph.
“PSI’s Io Input/Output Observatory detects large volcanic eruption on Jupiter’s moon Io.” Institute of Planetology.
Featured image: IoIO image of Io’s sodium nebula during an eruption. Credit: Jeff Morgenthaler, PSI.