posted on 2019-10-14, 10:45authored byT Cavalié, V Hue, P Hartogh, R Moreno, E Lellouch, H Feuchtgruber, C Jarchow, T Cassidy, LN Fletcher, F Billebaud, M Dobrijevic, L Rezac, GS Orton, M Rengel, T Fouchet, S Guerlet
Context. The origin of water in the stratospheres of Giant Planets has been an outstanding question ever since its first detection by ISO some 20 years ago. Water can originate from interplanetary dust particles, icy rings and satellites and large comet impacts. Analysis of Herschel Space Observatory observations have proven that the bulk of Jupiter's stratospheric water was delivered by the Shoemaker-Levy 9 impacts in 1994. In 2006, the Cassini mission detected water plumes at the South Pole of Enceladus, placing the moon as a serious candidate for Saturn's stratospheric water. Further evidence was found in 2011, when Herschel demonstrated the presence of a water torus at the orbital distance of Enceladus, fed by the moon's plumes. Finally, water falling from the rings onto Saturn's uppermost atmospheric layers at low latitudes was detected during the final orbits of Cassini's end-of-mission plunge into the atmosphere. Aims. In this paper, we use Herschel mapping observations of water in Saturn's stratosphere to identify its source. Methods. Several empirical models are tested against the Herschel-HIFI and -PACS observations, which were collected on December 30, 2010, and January 2nd, 2011 (respectively). Results. We demonstrate that Saturn's stratospheric water is not uniformly mixed as a function of latitude, but peaking at the equator and decreasing poleward with a Gaussian distribution. We obtain our best fit with an equatorial mole fraction 1.1 ppb and a half-width at half-maximum of 25{\deg}, when accounting for a temperature increase in the two warm stratospheric vortices produced by Saturn's Great Storm of 2010-2011. Conclusions. This work demonstrates that Enceladus is the main source of Saturn's stratospheric water.
Funding
This work was supported by the Programme National de
Planétologie (PNP) of CNRS/INSU, co-funded by CNES. T.C. was supported
by a CNES fellowship at the beginning of this work. Support for G.S.O.
was provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology. PACS was developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria);
KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany);
INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESAPRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy),
and CICYT/MCYT (Spain). HIFI was designed and built by a consortium of
institutes and university departments from across Europe, Canada and the United
States under the leadership of SRON Netherlands Institute for Space Research,
Groningen, The Netherlands and with major contributions from Germany, France
and the USA. Consortium members are: Canada: CSA, U.Waterloo; France:
CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland,
NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di ArcetriINAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio
Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA). Sweden:
Chalmers University of Technology – MC2, RSS & GARD; Onsala Space
Observatory; Swedish National Space Board, Stockholm University – Stockholm
Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. The
Herschel spacecraft was designed, built, tested, and launched under a contract
to ESA managed by the Herschel/Planck Project team by an industrial consortium under the overall responsibility of the prime contractor Thales Alenia Space
(Cannes), and including Astrium (Friedrichshafen) responsible for the payload
module and for system testing at spacecraft level, Thales Alenia Space (Turin)
responsible for the service module, a
History
Citation
Astronomy and Astrophysics, 2019, 630, A87
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
Version
VoR (Version of Record)
Published in
Astronomy and Astrophysics
Publisher
EDP Sciences for European Southern Observatory (ESO)