Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign
The past decades of Cassini’s investigation around Saturn have revealed the frequent occurrence of ∼1 hr quasiperiodic (QP) signatures in the in situ magnetic field and plasma measurements and plasma wave observations. Saturn’s aurora, as the response to the planet’s magnetospheric dynamics, is also...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/adce06 |
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| author | Tianshu Qin Sarah V. Badman Zhonghua Yao Yan Xu Elias Roussos |
| author_facet | Tianshu Qin Sarah V. Badman Zhonghua Yao Yan Xu Elias Roussos |
| author_sort | Tianshu Qin |
| collection | DOAJ |
| description | The past decades of Cassini’s investigation around Saturn have revealed the frequent occurrence of ∼1 hr quasiperiodic (QP) signatures in the in situ magnetic field and plasma measurements and plasma wave observations. Saturn’s aurora, as the response to the planet’s magnetospheric dynamics, is also observed to exhibit transient features that can reoccur with a strikingly similar periodicity. Previous investigations have associated these features with energetic plasma injections, standing Alfvén waves, and dayside magnetodisk reconnections, which all require a closed-field configuration. However, both previous and our analyses of the Hubble Space Telescope (HST) images, as Saturn approached the equinox (when both poles are in the field of view), reveal that transient auroral emissions are strictly nonconjugate between hemispheres—they occur in either the north or south alone. This picture is matchable with the open-configured, north–south asymmetric magnetopause reconnection. We also present a detailed case analysis of Cassini’s measurements for a prolonged period before and after a sequence of transient auroral brightenings observed in HST’s visits G1–G4. We show that the northern lobe featured hourly QP pulsations in the magnetic field, electron flux, and whistler-mode hiss. In an interval outside HST exposures, we observed tens to hundreds of keV electrons in the antiparallel direction associated with upward field-aligned currents, which can in turn produce aurora. This is potentially suggestive of reconnection processes at the magnetopause, but are limited in the spatial scale. |
| format | Article |
| id | doaj-art-03edc5fc9b874d3ea341096daa5693ef |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-03edc5fc9b874d3ea341096daa5693ef2025-08-20T02:40:29ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01985111610.3847/1538-4357/adce06Saturn’s Recurrent Auroral Flashes in the Equinoctial CampaignTianshu Qin0https://orcid.org/0000-0001-8870-8350Sarah V. Badman1https://orcid.org/0000-0002-2041-1507Zhonghua Yao2https://orcid.org/0000-0001-6826-2486Yan Xu3https://orcid.org/0000-0002-2542-9001Elias Roussos4https://orcid.org/0000-0002-5699-0678NWU-HKU Joint Center of Earth and Planetary Sciences, Department of Earth Sciences, The University of Hong Kong , Hong Kong SAR, People’s Republic of China; Lancaster University , Lancaster, UKLancaster University , Lancaster, UKNWU-HKU Joint Center of Earth and Planetary Sciences, Department of Earth Sciences, The University of Hong Kong , Hong Kong SAR, People’s Republic of ChinaDepartment of Earth and Space Sciences, Southern University of Science and Technology (SUSTech) , Shenzhen, People’s Republic of ChinaMax Planck Institute for Solar System Research , Göttingen, GermanyThe past decades of Cassini’s investigation around Saturn have revealed the frequent occurrence of ∼1 hr quasiperiodic (QP) signatures in the in situ magnetic field and plasma measurements and plasma wave observations. Saturn’s aurora, as the response to the planet’s magnetospheric dynamics, is also observed to exhibit transient features that can reoccur with a strikingly similar periodicity. Previous investigations have associated these features with energetic plasma injections, standing Alfvén waves, and dayside magnetodisk reconnections, which all require a closed-field configuration. However, both previous and our analyses of the Hubble Space Telescope (HST) images, as Saturn approached the equinox (when both poles are in the field of view), reveal that transient auroral emissions are strictly nonconjugate between hemispheres—they occur in either the north or south alone. This picture is matchable with the open-configured, north–south asymmetric magnetopause reconnection. We also present a detailed case analysis of Cassini’s measurements for a prolonged period before and after a sequence of transient auroral brightenings observed in HST’s visits G1–G4. We show that the northern lobe featured hourly QP pulsations in the magnetic field, electron flux, and whistler-mode hiss. In an interval outside HST exposures, we observed tens to hundreds of keV electrons in the antiparallel direction associated with upward field-aligned currents, which can in turn produce aurora. This is potentially suggestive of reconnection processes at the magnetopause, but are limited in the spatial scale.https://doi.org/10.3847/1538-4357/adce06SaturnAuroraePlanetary magnetospheres |
| spellingShingle | Tianshu Qin Sarah V. Badman Zhonghua Yao Yan Xu Elias Roussos Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign The Astrophysical Journal Saturn Aurorae Planetary magnetospheres |
| title | Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign |
| title_full | Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign |
| title_fullStr | Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign |
| title_full_unstemmed | Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign |
| title_short | Saturn’s Recurrent Auroral Flashes in the Equinoctial Campaign |
| title_sort | saturn s recurrent auroral flashes in the equinoctial campaign |
| topic | Saturn Aurorae Planetary magnetospheres |
| url | https://doi.org/10.3847/1538-4357/adce06 |
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