1. Southwest Research Institute, San Antonio, Texas 78228, USA
2. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
3. Department of Earth and Planetary Sciences, Washington University, St Louis, Missouri 63130, USA
4. School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, USA
5. Observatoire de Besançon, Institut UTINAM, CNRS-UMR 6213, BP 1615, 25010 Besançon Cedex, France
6. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
7. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland 20723, USA
8. Institutes of Astronomy and Space Science, National Central University, Chung Li 32054, Taiwan

Correspondence to: W. S. Lewis¹ Correspondence and requests for materials should be addressed to W.S.L. (Email: wlewis@swri.edu).

Abstract

Jets of water ice from surface fractures near the south pole¹ of Saturn's icy moon Enceladus produce a plume of gas and particles^{2, 3, 4, 5}. The source of the jets may be a liquid water region under the ice shell—as suggested most recently by the discovery of salts in E-ring particles derived from the plume⁶—or warm ice that is heated, causing dissociation of clathrate hydrates⁷. Here we report that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, ⁴⁰Ar. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180 K have been measured near the fractures from which the jets emanate⁸. We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.

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