[en] The most intense auroral emissions from Earth's polar regions, called discrete for their sharply defined spatial configurations, are generated by a process involving coherent acceleration of electrons by slowly evolving, powerful electric fields directed along the magnetic field lines that connect Earth's space environment to its polar regions. In contrast, Earth's less intense auroras are generally caused by wave scattering of magnetically trapped populations of hot electrons (in the case of diffuse aurora) or by the turbulent or stochastic downward acceleration of electrons along magnetic field lines by waves during transitory periods (in the case of broadband or Alfvénic aurora). Jupiter's relatively steady main aurora has a power density that is so much larger than Earth's that it has been taken for granted that it must be generated primarily by the discrete auroral process. However, preliminary in situ measurements of Jupiter's auroral regions yielded no evidence of such a process. Here we report observations of distinct, high-energy, downward, discrete electron acceleration in Jupiter's auroral polar regions. We also infer upward magnetic-field-aligned electric potentials of up to 400 kiloelectronvolts, an order of magnitude larger than the largest potentials observed at Earth. Despite the magnitude of these upward electric potentials and the expectations from observations at Earth, the downward energy flux from discrete acceleration is less at Jupiter than that caused by broadband or stochastic processes, with broadband and stochastic characteristics that are substantially different from those at Earth.
Research Center/Unit :
STAR - Space sciences, Technologies and Astrophysics Research - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Mauk, B. H.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Haggerty, D. K.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Paranicas, C.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Clark, G.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Kollmann, P.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Rymer, A. M.; The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
Bolton, S. J.; Southwest Research Institute, San Antonio, Texas, USA
Levin, S. M.; Jet Propulsion Laboratory, Pasadena, California, USA
Adriani, A.; Instituto Nazionale di Astrofisica-Instituo di Astofisica e Planetologia Spaziali, Roma, Italy
Allegrini, F.; Southwest Research Institute, San Antonio, Texas, USA ; Physics and Astronomy Department, University of Texas at San Antonio, San Antonio, Texas, USA
Bagenal, F.; University of Colorado, Boulder, Colorado, USA
Bonfond, Bertrand ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Connerney, J. E. P.; NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Gladstone, G. R.; Southwest Research Institute, San Antonio, Texas, USA
Kurth, W. S.; University of Iowa, Iowa City, Iowa, USA
McComas, D. J.; Southwest Research Institute, San Antonio, Texas, USA ; Princeton University, Princeton, New Jersey, USA
Valek, P.; Southwest Research Institute, San Antonio, Texas, USA)
Ergun, R. E. et al. FAST satellite observations of electric field structures in the auroral zone. Geophys. Res. Lett. 25, 2025-2028 (1998).
Carlson, C. W., Pfaff, R. F. & Watzin, J. G. The Fast Auroral SnapshoT (FAST) mission. Geophys. Res. Lett. 25, 2013-2016 (1998).
Chaston, C. C. et al. The turbulent Alfvénic aurora. Phys. Rev. Lett. 100, 175003 (2008).
Amm, O. et al. Chapter 4: in situ measurements in the auroral plasma. Space Sci. Rev. 103, 93-208 (2002).
Cowley, S. W. H. & Bunce, E. J. Origin of the main auroral oval in Jupiter's coupled magnetosphere-ionosphere system. Planet. Space Sci. 49, 1067-1088 (2001).
Hill, T. W. The Jovian auroral oval. J. Geophys. Res. 106, 8101-8107 (2001).
Ray, L. C., Ergun, R. E., Delamere, P. A. & Bagenal, F. Magnetosphere-ionosphere coupling at Jupiter: effect of field-aligned potentials on angular momentum transport. J. Geophys. Res. 115, A09211 (2010).
Connerney, J. E. P. et al. Jupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits. Science 356, 826-832 (2017).
Mauk, B. H. et al. Juno observations of energetic charged particles over Jupiter's polar regions: analysis of monodirectional and bidirectional electron beams. Geophys. Res. Lett. 44, 4410-4418 (2017).
Allegrini, F. et al. Electron beams and loss cones in the auroral regions of Jupiter. Geophys. Res. Lett. 44, http://doi.org/10.1002/2017GL073180 (2017).
Arnoldy, R. L. in Physics of Auroral Arc Formation (eds Akasofu, S.-I. & Kan, J. R.) 56-66 (AGU, 1981).
Gérard, J.-C. et al. Mapping the electron energy in Jupiter's aurora: Hubble spectral observations. J. Geophys. Res. 119, 9072-9088 (2014).
Gustin, J. et al. Characteristics of north Jovian aurora from STIS FUV spectral images. Icarus 268, 215-241 (2016).
Tao, C. et al. Variation of Jupiter's aurora observed by Hisaki/EXCEED: 2. Estimation of auroral parameters and magnetospheric dynamics. J. Geophys. Res. 121, 4055-4071 (2016).
Mauk, B. H. et al. The Jupiter Energetic Particle Detector Instrument (JEDI) investigation for the Juno mission. Space Sci. Rev. http://doi.org/10.1007/s11214-013-0025-3 (2013).
Bonfond, B. et al. Morphology of the UV aurorae Jupiter during Juno's first perijove observations. Geophys. Res. Lett. 44, 4463-4471 (2017).
McComas, D. J. et al. The Jovian Auroral Distributions Experiment (JADE) on the Juno mission to Jupiter. Space Sci. Rev. http://doi.org/10.1007/s11214-013-9990-9 (2013).
Krall, N. A. & Trivelpiece, A. W. Principles of Plasma Physics Ch. 3 (McGraw-Hill, 1973).
Grodent, D. et al. Jupiter's polar auroral emissions. J. Geophys. Res. 108, 1366 (2003).
Janhunen, J., Olsson, A., Russell, C. T. & Laakso, H. Alfvénic electron acceleration in aurora occurs in global Alfvén resonosphere region. Space Sci. Rev. 122, 89-95 (2006).
Connerney, J. E. P. et al. The Juno magnetic field investigation. Space Sci. Rev. https://doi.org/10.1007/s11214-017-0334-z (2017).
Connerney, J. E. P., Acuña, M. H., Ness, N. F. & Satoh, T. New models of Jupiter's magnetic field constrained by the Io flux tube footprint. J. Geophys. Res. 103, 11929-11939 (1998).
Gladstone, G. R. et al. The ultraviolet spectrograph on NASA's Juno mission. Space Sci. Rev. https://doi.org/10.1007/s11214-014-0040-z (2014).
Hess, S. L. G., Bonfond, B., Zarka, P. & Grodent, D. Model of the Jovian magnetic field topology constrained by the Io auroral emissions. J. Geophys. Res. 116, A05217 (2011).
Mauk, B. H. et al. Energetic ion characteristics and neutral gas interactions in Jupiter's magnetosphere. J. Geophys. Res. 109, A09S12 (2004).
Bolton, J. S. et al. Jupiter's interior and deep atmosphere: the initial pole-topole passes with the Juno spacecraft. Science 356, 821-825 (2017).
