Editor's Summary

25 June 2009

An ocean on Enceladus ocean: the sodium test


Images from the Cassini spacecraft showed erupting plumes of water vapour and ice particles on Saturn's moon Enceladus, prompting speculation a subsurface ocean might be acting as a source of liquid water. Two groups this week report evidence relevant to the search for this subsurface ocean. The results, at first sight contradictory, leave the ocean a possibility, though still a hypothetical one. Postberg et al. used the Cassini Cosmic Dust Analyser to determine the chemical composition of ice grains in Saturn's E-ring, which consists largely of material from Enceladus. They find a population of E-ring grains rich in sodium salts, which should be possible only if the plumes originate from liquid water. Schneider et al. used Earth-based spectroscopic telescopes to search for sodium emission in the gas plumes erupting from Enceladus and found none. This is inconsistent with a direct supply from a salty ocean and suggests alternative eruption sources such as a deep ocean, a freshwater reservoir or ice. Or if there is a salty reservoir of water, some process not yet determined must be preventing the sodium from escaping into space.

News and ViewsPlanetary science: Enceladus with a grain of salt

The observation that water plumes erupt from cracks on Saturn's moon Enceladus has fired speculation about a possible subsurface ocean. The latest searches for sodium salts point to the existence of such an ocean.

John Spencer

doi:10.1038/4591067a

LetterSodium salts in E-ring ice grains from an ocean below the surface of Enceladus

F. Postberg, S. Kempf, J. Schmidt, N. Brilliantov, A. Beinsen, B. Abel, U. Buck & R. Srama

doi:10.1038/nature08046

LetterNo sodium in the vapour plumes of Enceladus

Nicholas M. Schneider, Matthew H. Burger, Emily L. Schaller, Michael E. Brown, Robert E. Johnson, Jeffrey S. Kargel, Michele K. Dougherty & Nicholas A. Achilleos

doi:10.1038/nature08070