Discrete and broadband electron acceleration in Jupiter’s powerful aurora
The process that generates Earth’s most intense aurora is found to occur at Jupiter, but is of only secondary importance in generating Jupiter’s much more powerful aurora. Jupiter's awesome aurora The most intense aurora on Earth are generated by a 'discrete' process whereby electrons...
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| Vydáno v: | Nature (London) Ročník 549; číslo 7670; s. 66 - 69 |
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| Hlavní autoři: | , , , , , , , , , , , , , , , , |
| Médium: | Journal Article |
| Jazyk: | angličtina |
| Vydáno: |
London
Nature Publishing Group UK
07.09.2017
Nature Publishing Group |
| Témata: | |
| ISSN: | 0028-0836, 1476-4687, 1476-4687 |
| On-line přístup: | Získat plný text |
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| Shrnutí: | The process that generates Earth’s most intense aurora is found to occur at Jupiter, but is of only secondary importance in generating Jupiter’s much more powerful aurora.
Jupiter's awesome aurora
The most intense aurora on Earth are generated by a 'discrete' process whereby electrons are accelerated coherently. Weaker aurora arise from wave scattering of magnetically trapped electrons. As Jupiter's aurora is orders of magnitude more powerful than Earth's, it was naturally assumed that the former process was responsible, yet early
in situ
observations by the Juno spacecraft found no evidence of the discrete process. Barry Mauk and collaborators report discrete downward accelerations of electrons on some auroral crossings, but the energy flux is much less than that caused by broadband processes, with broadband characteristics that are very different from those at Earth.
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
1
,
2
. 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)
3
,
4
. 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
5
,
6
,
7
. However, preliminary
in situ
measurements of Jupiter’s auroral regions yielded no evidence of such a process
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,
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,
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. 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
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. 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. |
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| Bibliografie: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23 scopus-id:2-s2.0-85029032972 |
| ISSN: | 0028-0836 1476-4687 1476-4687 |
| DOI: | 10.1038/nature23648 |