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<\/a><\/p>\nNASA; JPL-Caltech; SwRI; ASI; INAF; JIRAM<\/p>\n
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NASA; JPL-Caltech; SwRI; ASI; INAF; JIRAM<\/p>\n
\u00d7<\/a><\/p>\n The Juno space probe has spent the past nine years observing Jupiter and its moons. As the spacecraft\u2019s mission draws to a close, the precession of its orbit has caused its closest approach to the gas giant to shift toward the north pole, enabling it to uncover a surprise: an unusual pattern of plasma waves in the planet\u2019s magnetosphere. Now Robert Lysak of the University of Minnesota and his colleagues describe these waves and propose a mechanism for generating them [1<\/a>]. Their theory offers a new component to include in planetary magnetosphere models and opens a new plasma regime to further exploration.<\/p>\n According to textbook plasma physics, collective waves of electrons in a plasma called Langmuir waves tend to oscillate parallel to magnetic-field lines at a so-called plasma frequency that\u2019s much greater than the ions\u2019 angular frequency around these field lines, their gyrofrequency. Meanwhile, ions tend to oscillate perpendicular to magnetic-field lines as Alfv\u00e9n waves, with an upper frequency limit corresponding to the ion gyrofrequency. The waves detected by Juno, however, departed from that paradigm: The Alfven waves\u2019 frequency extended only to the plasma frequency, which was less than the ion gyrofrequency. And the waves\u2019 frequency never exceeded the plasma frequency.<\/p>\n To account for the observed waves, Lysak and his colleagues analyzed the relationship between the waves\u2019 frequency and wave number in the highly magnetized, low-density plasma of Jupiter\u2019s magnetosphere and described a scenario in which Alfv\u00e9n waves transitioned to Langmuir waves at large wave numbers. This behavior can be spurred by upward-propagating electron beams, with energies from 1 keV to 2 MeV. Juno first observed such beams in Jupiter\u2019s northern polar regions in 2016.<\/p>\n The researchers say that this scenario should interest astronomers studying magnetized stars and exoplanets that have intrinsic magnetic fields.<\/p>\n \u2013Rachel Berkowitz<\/p>\n Rachel Berkowitz is a Corresponding Editor for Physics Magazine\u00a0<\/a>based in Vancouver, Canada.<\/p>\n ReferencesR. L. Lysak et al., \u201cNew plasma regime in Jupiter\u2019s auroral zones,\u201d Phys. Rev. Lett. 135, 035201 (2025)<\/a>.Subject AreasPlasma Physics<\/a>Astrophysics<\/a>Related Articles A mechanism for accelerating charged particles in astrophysical plasmas has been reproduced with cold atoms in an optical trap. Read More \u00bb<\/a><\/p>\n<\/a><\/a><\/a>Atomic and Molecular PhysicsMimicking a Cosmic Accelerator<\/a>July 9, 2025<\/p>\n