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.)

SQUEEZED PHONONS HAVE BEEN PRODUCED for the first time, allowing researchers to temporarily reduce the uncertainties in the positions of atoms in a crystal. Classically, atoms in a crystal are like little balls which vibrate around their equilibrium positions in a lattice. The quantum-mechanical description of this motion is given in terms of particles called "phonons" which carry specific bundles of vibrational energy. According to quantum mechanics, an atom does not have a definite position, but a spread of possible positions. To temporarily reduce these fundamental uncertainties, a University of Michigan team (Roberto Merlin, 313-763-9759) has successfully altered the state of the phonons in a crystal to produce "squeezed" phonons, which act to momentarily reduce the uncertainty in the atoms' positions at the expense of greater uncertainties in the atoms' momenta. In the experiment, described at the March APS Meeting, researchers shine two 70-femtosecond laser pulses on a potassium tantalate crystal. The first pulse momentarily perturbs the frequencies of the individual phonons in the crystal. In classical terms, the net result is to return far-flung atoms closer to their central positions on the lattice while not affecting as much the others which are already close to their central positions. The second pulse measures the change of refractive index in the crystal caused by squeezing and this tells how much the atoms as a whole stray from their central positions. Theoretically predicted since the early 1990s (Update 261) by various groups, squeezed phonons are similar to the previously demonstrated phenomenon of squeezed light (Update 82). (Science, 14 March 1997.)

PROTON TRANSISTOR MEMORY. Electrons do most of the work in electronic devices; indeed heavier, mobile, positively-charged ions are usually a nuisance. A Sandia experiment, however, has made hydrogen ions (protons buried inside a semiconductor sandwich) into the primary carriers of information in a Si/SiO₂/Si device. Judged as a storage device, this transistor did pretty well: it retained its state (on or off) for up to 25 hours, it successfully underwent 10,000 write-erase cycles, and could be switched on a 50-msec timescale. Its chief virtue may prove to be its ease of construction. (K. Vanheusden et al., Nature, 10 April 1997.)