Premium
Cassini UVIS Detection of Saturn's North Polar Hexagon in the Grand Finale Orbits
Author(s) -
Pryor W. R.,
Esposito L. W.,
Jouchoux A.,
West R. A.,
Grodent D.,
Gérard J.C.,
Radioti A.,
Lamy L.,
Koskinen T.
Publication year - 2019
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1029/2019je005922
Subject(s) - saturn , polar , spectrograph , physics , ultraviolet , haze , astronomy , astrobiology , astrophysics , planet , optics , spectral line , meteorology
Cassini's final orbits in 2016 and 2017 provided unprecedented spatial resolution of Saturn's polar regions from near‐polar spacecraft viewing geometries. Long‐wavelength channels of Cassini's Ultraviolet Imaging Spectrograph instrument detected Saturn's UV‐dark north polar hexagon near 180 nm at planetocentric latitudes near 75°N. The dark polar hexagon is surrounded by a larger, less UV‐dark collar poleward of planetocentric latitude 65°N associated with the dark north polar region seen in ground‐based images. The hexagon is closely surrounded by the main arc of Saturn's UV aurora. The UV‐dark material was locally darkest on one occasion (23 January 2017) at the boundary of the hexagon; in most Ultraviolet Imaging Spectrograph images the dark material more uniformly fills the hexagon. The observed UV‐dark stratospheric material may be a hydrocarbon haze produced by auroral ion‐neutral chemistry at submicrobar pressure levels. Ultraviolet Imaging Spectrograph polar observations are sensitive to UV‐absorbing haze particles at pressures lower than about 10–20 mbar.