Volume 630, October 2019
|Number of page(s)||15|
|Section||Planets and planetary systems|
|Published online||26 September 2019|
Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus★
Laboratoire d’Astrophysique de Bordeaux, University of Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire,
2 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC University of Paris 06, Université Paris Diderot, Sorbonne Paris Cité, 92195 Meudon, France
3 Southwest Research Institute, San Antonio, TX 78228, USA
4 Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany
5 Max Planck Institut für Extraterrestrische Physik, Garching, Germany
6 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
7 Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
8 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
9 Sorbonne Universités, UPMC Paris 06, UMR 8539, LMD, 75005 Paris, France
Accepted: 23 July 2019
Context. The origin of water in the stratospheres of giant planets has been an outstanding question ever since its first detection by the Infrared Space Observatory some 20 years ago. Water can originate from interplanetary dust particles, icy rings and satellites, and large comet impacts. Analyses 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, which made the moon 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 that was 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. We tested several empirical models against the Herschel-HIFI and -PACS observations, which were collected on December 30, 2010, and January 2, 2011, respectively.
Results. We demonstrate that Saturn’s stratospheric water is not uniformly mixed as a function of latitude, but peaks at the equator and decreases 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°, 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.
Key words: planets and satellites: individual: Saturn / planets and satellites: individual: Enceladus / planets and satellites: atmospheres
© T. Cavalié et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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