Letters to Nature

Nature 391, 363-365 (22 January 1998) | doi:10.1038/34857; Received 19 May 1997; Accepted 5 November 1997

Evidence for a subsurface ocean on Europa

Michael H. Carr1, Michael J. S. Belton2, Clark R. Chapman3, Merton E. Davies4, Paul Geissler5, Richard Greenberg5, Alfred S. McEwen5, Bruce R. Tufts5, Ronald Greeley6, Robert Sullivan7, James W. Head8, Robert T. Pappalardo8, Kenneth P. Klaasen9, Torrence V. Johnson9, James Kaufman9, David Senske9, Jeffrey Moore10, Gerhard Neukum11, Gerald Schubert12, Joseph A. Burns7, Peter Thomas7 & Joseph Veverka7

  1. US Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA
  2. National Optical Astronomy Observatory, 950 Cherry Street, Tucson, Arizona 85719, USA
  3. Southwest Research Institute, 1050 Walnut Street, Boulder, Colorado 8030, USA
  4. Rand Corporation, 1700 Main Street, Santa Monica, California 90406, USA
  5. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
  6. Geology Department, Arizona State University, Tempe, Arizona 85287, USA
  7. Cornell University, Ithaca, New York 14853, USA
  8. Geology Department, Brown University, Providence, Rhode Island 02912, USA
  9. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 911909, USA
  10. NASA/Ames Research Center, Moffet Field, California 94035, USA
  11. DLR-Institut für Planetenerkundung, Rudower Chaussee 5, 12489 Berlin, Germany
  12. Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA

Correspondence to: Michael H. Carr1 Correspondence and requests for materials should be addressed to M.H.C. (e-mail: Email: carr@astmnl.wr.usgs.gov).

Ground-based spectroscopy of Jupiter's moon Europa, combined with gravity data, suggests that the satellite has an icy crust roughly 150 km thick and a rocky interior1, 2, 3, 4. In addition, images obtained by the Voyager spacecraft revealed that Europa's surface is crossed by numerous intersecting ridges and dark bands (called lineae) and is sparsely cratered, indicating that the terrain is probably significantly younger than that of Ganymede and Callisto5. It has been suggested that Europa's thin outer ice shell might be separated from the moon's silicate interior by a liquid water layer, delayed or prevented from freezing by tidal heating6, 7, 8, 9, 10; in this model, the lineae could be explained by repetitive tidal deformation of the outer ice shell11, 12, 13. However, observational confirmation of a subsurface ocean was largely frustrated by the low resolution (>2 km per pixel) of the Voyager images14. Here we present high-resolution (54 m per pixel) Galileo spacecraft images of Europa, in which we find evidence for mobile 'icebergs'. The detailed morphology of the terrain strongly supports the presence of liquid water at shallow depths below the surface, either today or at some time in the past. Moreover, lower-resolution observations of much larger regions suggest that the phenomena reported here are widespread.