Io Outburst Shines in Plasma Torus

Between September and December 2022, a small telescope in the Arizona desert observed a brightening of the plasma torus caused by Io’s charged volcanic particles.

Beth Johnson

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IMAGE: The volcano-laced surface of Jupiter’s moon Io was captured in infrared by the Juno spacecraft’s Jovian Infrared Auroral Mapper (JIRAM) imager as it flew by at a distance of about 80,000 kilometers on July 5, 2022. Brighter spots indicate higher temperatures in this image. CREDIT: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

I love Io. It’s my favorite moon not orbiting the Earth and is endlessly fascinating.

Io is incredibly volcanic and is often referred to as the ‘most volcanic body in the solar system’, which may not be true and is still debated, but it sure sounds cool. Or hot. Something neat. No matter the answer to that debate, Io has a lot of volcanos — over 400 of them; however, they are not caused by plate tectonics like volcanos are on Earth. Due to the tidal heating caused by Jupiter as well as the other Galilean moons, Io’s interior stays hot enough to create magma and gets fractures by the constant cooling and heating for that magma to breach the surface. All those eruptions on Io send particles into space, and those particles have caused several different observed phenomena.

Back in 2021, researchers led by George Clark analyzed data from NASA’s Juno spacecraft and found that Io is, in fact, a particle accelerator for Jupiter. All those volcanic particles start out by forming an exceedingly thin atmosphere around the tiny moon; it’s so thin that it’s technically an exosphere and not an atmosphere! From there, the particles interact with charged particles surrounding Jupiter and end up charged themselves and then swept into the powerful magnetic field lines. Basically, an electric circuit is formed between Io and Jupiter, stretching over 400,000 kilometers.

IMAGE: A close-up image of Jupiter’s aurora, taken in ultraviolet light by the Hubble Space Telescope in 1998. Peripheral to Jupiter’s main aurora are the auroral spots or “footprints” where electric currents from Jupiter’s moons Io, Europa, and Ganymede rain electrons down onto the planet’s upper atmosphere. CREDIT: Modified from NASA/STSci/AURA

And where that circuit interacts with Jupiter’s atmosphere, the particles actually create an auroral footprint that has been seen in ultraviolet images taken by the Hubble Space Telescope in 1998. When Juno passed close to that region during its twelfth flyby (or perijove), an instrument called the Jupiter Energetic Particle Detector Instrument (JEDI) managed to detect protons that were zooming back from Jupiter to Io at about 50 million kilometers per hour. Clark noted in the press release: It’s the first

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Beth Johnson

Planetary scientist, podcast host. Communication specialist for SETI Institute and Planetary Science Institute. Buy me a coffee: https://ko-fi.com/planetarypan