ICEBERGS AND OCEANS ON EUROPA . Previous pictures suggested that Jupiter's moon was covered with an Arctic-like fractured ice sheet. Now ever sharper images reveal what look like detached icebergs that can be traced back to earlier lodgements. Scientists associated with the Galileo spacecraft, which viewed Europa on the closest-ever encounter (586 km) in February, believe that the turned-around ice blocks are probably floating on an ocean kept at least partially liquid by tidal forces from Jupiter or possibly from heat generated by internal radioactivity. The relative lack of impact craters and the extensive scarring imply, furthermore, that the icy surface is young (millions of years) and in places thin (several km). The last time a new ocean was reported, one scientist mused, was five hundred years ago when Balboa supposedly discovered the Pacific. (Jet Propulsion Lab press conference and press release, 9 April; JPL Galileo Home Page has images of Europa Ice Rafts.)