Using data collected by NASA’s Juno spacecraft as it flew past Jupiter’s highly volcanic moon Io in late 2023 and again in early 2024, a Southwest Research Institute-led team identified electrons with energies enhanced by processes in the region connecting the moon to Jupiter’s ionosphere, called an Alfvén wing. A paper published in Geophysical Research Letters emphasizes how these electrons, and their variation within that region, shape the plasma environment around Io.
“These electrons gain energy from the interaction between Io and Jupiter’s magnetic field,” said Dr. Robert Ebert, lead author of the paper. “These energized electrons then interact with Io’s atmosphere and surface, ionizing and exciting atoms and molecules and even creating aurora.”
In the 1990s, NASA’s Galileo mission discovered the presence of intense electron beams within the Alfvén wing and other regions near Io. These electrons can travel along the local magnetic field and interact with Io’s atmosphere. New results from Juno indicate that the electron properties within Io’s Alfvén wing are not uniform. The number of electrons in these beams are largest at the boundaries of the wing and weaker inside, suggesting that their interaction with Io might also vary across the moon.
Juno’s extended mission includes explorations of some of its many moons. This study focuses on plasma observations from the SwRI-led Jovian Auroral Distributions Experiment (JADE) as Juno flew by Io on Dec. 30, 2023, and Feb. 3, 2024.
(Top panels) X-Y projection of Juno’s Io flyby prior to (a) PJ57 and (c) PJ58 in the IPhiO coordinate system. Overplotted along the trajectory is the electron differential energy flux summed from 200 eV–32 keV. Data above (below) the black trajectory line denotes electrons streaming toward (away from) Io. The magnitude of the integrated flux is represented by both the color and thickness of the symbols. The black flow streamlines are adapted from Saur et al. (1999). The gray circles offset from Io (top panels) represent modeled cross-sections of the Alfvén wing at Juno’s location. (Bottom panels) Y-Z projection of Juno’s Io flyby for (b) PJ57 and (d) PJ58. The purple regions represent the orientation of the magnetic field connected to Io at the time of the flybys. © Geophysical Research Letters (2025). DOI: 10.1029/2024GL114183
“It is amazing to see that JADE was able to make new, high-resolution measurements in this region of Jupiter’s harsh radiation environment,” said Dr. Frederic Allegrini, JADE instrument lead and second author of the paper. “Any instrument or spacecraft would stop functioning after a short exposure time if it were to stay there rather than fly through it.”
The Juno observations confirmed the continuous presence of electron beams in the Alfvén wing over Io’s pole and their presence beyond the distance where Galileo explored. These beams travel along Jupiter’s magnetic field, impacting Io or its atmosphere when on magnetic field lines that have one foot connected to Io.
“These spatially variable beams are more energized than electrons in the nearby Io torus, a donut-shaped cloud of electrically charged gas surrounding Jupiter,” Ebert said. “Their location within and around the Alfvén wing must be considered when interpreting their impact on Io’s atmosphere and nearby plasma environment.”
The Juno mission is led by SwRI Associate Vice President Dr. Scott Bolton.
More information:
R. W. Ebert et al, Spatially Variable Electron Beams in Io’s Northern Alfvén Wing and Downstream Region, Geophysical Research Letters (2025). DOI: 10.1029/2024GL114183
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Southwest Research Institute
Citation:
Scientists identify unexpected variations in electrons connecting Jupiter with its moon Io (2025, March 11)
