Callistan ocean
Indeed, the Galileo Magnetometer has returned some persuasive data.
See
Induced magnetic fields as evidence for subsurface oceans in Europa and Callisto
K. Khurana, M. G. Kivelson, D. J. Stevenson, G. Schubert, C. T. Russell, R. J. Walker, C. Polanskey
Nature 395, 777 - 780 (22 October 1998)
and
http://www.jpl.nasa.gov/galileo/news32.html
Alex R. Blackwell
University of Hawaii
