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Plasma and Magnetic Field Properties in Europa's Wake From Juno.

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Title: Plasma and Magnetic Field Properties in Europa's Wake From Juno.
Authors: Ebert, R. W.1,2 (AUTHOR) rebert@swri.edu, Allegrini, F.1,2 (AUTHOR), Szalay, J. R.3 (AUTHOR), Pontoni, A.1 (AUTHOR), Saur, J.4 (AUTHOR), Bagenal, F.5 (AUTHOR), Bolton, S. J.1 (AUTHOR), Connerney, J. E. P.6,7 (AUTHOR), DiBraccio, G. A.7 (AUTHOR), Howard, S. K.7,8 (AUTHOR), McComas, D. J.3 (AUTHOR), Valek, P.1 (AUTHOR), Wilson, R. J.5 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. May2025, Vol. 130 Issue 5, p1-13. 13p.
Subject Terms: Europa (Satellite), Juno (Space probe), Ion sources, Space environment, Electron temperature measurement
Abstract: We present a comprehensive synthesis of plasma and magnetic field observations during Juno's flyby through Europa's wake on 29 September 2022, which has a closest approach distance of 353 km. Compared to Galileo, Juno includes measurements of plasma electrons and mass‐per‐charge resolved ions. This allows for characterization of the thermal electron environment near Europa and definitive identification of the ion species present in that region. The plasma and magnetic field properties bounding Europa's wake are similar to conditions at Europa's orbit from Voyager and Galileo. While the ion flow patterns within the wake and accelerated flows along Europa's flank are consistent with the Galileo E4 wake flyby, the ion flows slowed more, reaching a low of 65 km s−1 near the wake center, and the ion densities near closest approach are ∼4 times higher (∼170–190 cm−3) as Juno's flyby occurred closer to Europa. The H+ and H2+ densities peaked near closest approach while heavy ion densities peaked near the wake center. These measurements quantify the modification of Jupiter's plasma disk composition by fresh injection of pickup ions. Properties of 0.032–32 keV electrons such as temperature, thermal pressure, and beta are reported for the first time in Europa's wake, the electron temperature reaching a low of ∼35 eV in the wake center, compared to 70–80 eV in Jupiter's nearby plasma disk. The components of the magnetic field are variable throughout the wake, the magnetic pressure being at least a factor 40 larger than the electron thermal pressure. Plain Language Summary: Charged particles from Jupiter's magnetosphere flow over and around Jupiter's moon Europa, impacting its surface and liberating neutral atoms. This interaction shapes the space environment around Europa and produces Europa's low density neutral atmosphere. The Juno spacecraft made a close flyby of Europa on 29 September 2022, transiting the region known as its wake. The low energy charged particle, or plasma, observations from Juno revealed a complex environment. The plasma flow was deflected and changed speed around the satellite, like the flow of water around an obstacle. The ion density showed enhancement in the wake, with protons and ions of molecular hydrogen having a maximum near closest approach and heavy ions, mainly oxygen, having their largest density near the wake center. These enhancements indicate that Europa is providing a source of ions in this region. Properties for electrons, such as their temperature and pressure, are measured in Europa's wake for the first time. These measurements revealed electron temperatures in the wake being significantly lower than in the plasma environment bounding that region. The pressure from the electrons was considerably less than that provided by Jupiter's magnetic field. Key Points: The plasma and magnetic field properties bounding Europa's wake are similar to conditions at Europa's orbit from previous missionsThe ion flows slowed more, and ion densities are higher compared to Galileo's E4 wake flyby, Juno's flyby occurring closer to EuropaThe electrons in the wake are cooler than in the plasma disk, their thermal pressure being ∼40 times less than the magnetic pressure [ABSTRACT FROM AUTHOR]
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Abstract:We present a comprehensive synthesis of plasma and magnetic field observations during Juno's flyby through Europa's wake on 29 September 2022, which has a closest approach distance of 353 km. Compared to Galileo, Juno includes measurements of plasma electrons and mass‐per‐charge resolved ions. This allows for characterization of the thermal electron environment near Europa and definitive identification of the ion species present in that region. The plasma and magnetic field properties bounding Europa's wake are similar to conditions at Europa's orbit from Voyager and Galileo. While the ion flow patterns within the wake and accelerated flows along Europa's flank are consistent with the Galileo E4 wake flyby, the ion flows slowed more, reaching a low of 65 km s−1 near the wake center, and the ion densities near closest approach are ∼4 times higher (∼170–190 cm−3) as Juno's flyby occurred closer to Europa. The H+ and H2+ densities peaked near closest approach while heavy ion densities peaked near the wake center. These measurements quantify the modification of Jupiter's plasma disk composition by fresh injection of pickup ions. Properties of 0.032–32 keV electrons such as temperature, thermal pressure, and beta are reported for the first time in Europa's wake, the electron temperature reaching a low of ∼35 eV in the wake center, compared to 70–80 eV in Jupiter's nearby plasma disk. The components of the magnetic field are variable throughout the wake, the magnetic pressure being at least a factor 40 larger than the electron thermal pressure. Plain Language Summary: Charged particles from Jupiter's magnetosphere flow over and around Jupiter's moon Europa, impacting its surface and liberating neutral atoms. This interaction shapes the space environment around Europa and produces Europa's low density neutral atmosphere. The Juno spacecraft made a close flyby of Europa on 29 September 2022, transiting the region known as its wake. The low energy charged particle, or plasma, observations from Juno revealed a complex environment. The plasma flow was deflected and changed speed around the satellite, like the flow of water around an obstacle. The ion density showed enhancement in the wake, with protons and ions of molecular hydrogen having a maximum near closest approach and heavy ions, mainly oxygen, having their largest density near the wake center. These enhancements indicate that Europa is providing a source of ions in this region. Properties for electrons, such as their temperature and pressure, are measured in Europa's wake for the first time. These measurements revealed electron temperatures in the wake being significantly lower than in the plasma environment bounding that region. The pressure from the electrons was considerably less than that provided by Jupiter's magnetic field. Key Points: The plasma and magnetic field properties bounding Europa's wake are similar to conditions at Europa's orbit from previous missionsThe ion flows slowed more, and ion densities are higher compared to Galileo's E4 wake flyby, Juno's flyby occurring closer to EuropaThe electrons in the wake are cooler than in the plasma disk, their thermal pressure being ∼40 times less than the magnetic pressure [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2024JA032520