Journal article
Saturn's Northern Aurorae at Solstice From HST Observations Coordinated With Cassini's Grand Finale
Geophysical research letters, Vol.45(18), pp.9353-9362
09/28/2018
DOI: 10.1029/2018GL078211
Abstract
Throughout 2017, the Hubble Space Telescope (HST) observed the northern far-ultraviolet aurorae of Saturn at northern solstice, during the Cassini Grand Finale. These conditions provided a complete viewing of the northern auroral region from Earth and a maximal solar illumination, expected to maximize the ionosphere-magnetosphere coupling. We analyze 24 HST images concurrently with Cassini measurements of Saturn's kilometric radiation and solar wind parameters predicted by two magnetohydrodynamic models. The aurorae reveal highly variable components, down to timescales of minutes, radiating 7 to 124 GW. They include a nightside-shifted main oval, unexpectedly frequent and bright cusp emissions, and a dayside low-latitude component. On average, these emissions display a strong local time dependence with two maxima at dawn and premidnight, the latter being newly observed and attributed to nightside injections possibly associated with solstice conditions. These results provide a reference frame to analyze Cassini in situ measurements, whether simultaneous or not.
Plain Language Summary In 2017, the Hubble Space Telescope regularly observed the northern ultraviolet aurorae of Saturn in coordination with Cassini in situ measurements obtained during the Grand Finale, when the spacecraft flew across magnetic field lines connected to the aurorae. Hubble imaged Saturn's aurorae at 24 occasions spread over 7months during northern solstice, when the northern auroral region was both fully visible from Earth and permanently illuminated by the Sun. The observed aurorae display a variety of components observed poleward of 68 degrees latitude with different properties, some of which were unreported before. These emissions strongly vary with time, down to a few minutes, and radiate from 7 to 124 GW. On average, the auroral intensity also strongly varies with local time (a Sun-referenced frame) and peaks at dawn, as previously observed, and also premidnight, pointing to a recurrent nightside activity of the magnetosphere. These results provide a reference basis to analyze Cassini in situ measurements.
Details
- Title: Subtitle
- Saturn's Northern Aurorae at Solstice From HST Observations Coordinated With Cassini's Grand Finale
- Creators
- L. Lamy - Laboratoire d’études spatiales et d’instrumentation en astrophysiqueR. Prange - Université de Versailles Saint-Quentin-en-YvelinesC. Tao - National Institute of Information and Communications TechnologyT. Kim - University of Alabama in HuntsvilleS. V. Badman - Lancaster UniversityP. Zarka - Laboratoire d’études spatiales et d’instrumentation en astrophysiqueB. Cecconi - Université de Versailles Saint-Quentin-en-YvelinesW. S. Kurth - University of IowaW. Pryor - Central Arizona CollegeE. Bunce - University of LeicesterA. Radioti - Space Sci Technol & Astrophys Res Inst, Liege, Belgium
- Resource Type
- Journal article
- Publication Details
- Geophysical research letters, Vol.45(18), pp.9353-9362
- Publisher
- Amer Geophysical Union
- DOI
- 10.1029/2018GL078211
- ISSN
- 0094-8276
- eISSN
- 1944-8007
- Number of pages
- 10
- Grant note
- CNRS/INSU program of Planetology (PNP) ST/N000749/1; ST/R000816/1; ST/M005534/1 / STFC; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC) CNRS/INSU program of Heliophysics (PNST) ST/R000816/1; ST/M005534/1 / Science and Technology Facilities Council; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC) ST/M005534/1 / STFC Ernest Rutherford Fellowship; UK Research & Innovation (UKRI); Science & Technology Facilities Council (STFC) 14811 / ESA/NASA Hubble Space Telescope (GO program) CNES; Centre National D'etudes Spatiales 1415150 / NASA; National Aeronautics & Space Administration (NASA) Jet Propulsion Laboratory
- Language
- English
- Date published
- 09/28/2018
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455363502771
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