Stress‐induced piezoelectric fields produce freely propagating electromagnetic radiation when microscopic rock fractures occur in quartz‐bearing rocks. A laboratory study is presented which shows that electromagnetic emissions are produced when microfractures occur in Westerly granite. A detailed model is presented for the emission process which allows an estimate of the total radiated power from an individual microfracture. On the basis of these results a case is presented that an unusual radio emission seen on several widely separated radio astronomy receivers in the northern hemisphere on May 16, 1960, was due to a stress‐induced microfracture along the Chilean fault. This radio event occurred 6 days prior to the great Chilean earthquake of May 22, 1960, and may have been a precursor to one of the largest earthquakes of this century.

16. We thank the entire Voyager team at NASA Headquarters and the Jet Propulsion Laboratory (JPL) for their support. We are especially grateful to R. Poynter for his invaluable assistance and support. We also thank E. Miner and J. Diner for their efforts to arrange the wideband coverage; J. Anderson, P. Jepsen, and G. Garneau for their assistance with the wideband data processing; C. Stembridge for his help in solving numerous problems; H. Bridge, J. Belcher, J. Scudder, and N. Ness for providing data in advance of publication and for their helpful discussions; and R. Anderson, R. West, L. Granroth, and R. Brechwald for carrying out the data reduction. The research at the University of Iowa was supported by NASA through contract 954013 with JPL, through grants NGL-16-001-002 and NGL-16-001-043 from NASA Headquarters, and by the Office of Naval Research. The research at TRW was supported by NASA through contract 954012 with JPL.

We report results from the first low-frequency radio receiver to be transported into the Jupiter magnetosphere. We obtained dramatic new information, both because Voyager was near or in Jupiter's radio emission sources and also because it was outside the relatively dense solar wind plasma of the inner solar system. Extensive radio spectral arcs, from above 30 to about 1 megahertz, occurred in patterns correlated with planetary longitude. A newly discovered kilometric wavelength radio source may relate to the plasma torus near Io's orbit. In situ wave resonances near closest approach define an electron density profile along the Voyager trajectory and form the basis for a map of the torus. Detailed studies are in progress and are outlined briefly.

The planetary radio astronomy experiment on board the Voyager spacecraft has detected bursts of nonthermal radio noise from Saturn occurring near 200 kilohertz, with a peak flux density comparable to higher frequency Jovian emissions. The radiation is right-hand polarized and is most likely emitted in the extraordinary magnetoionic mode from Saturn's northern hemisphere. Modulation that is consistent with a planetary rotation period of 10 hours 39.9 minutes is apparent in the data.

Detection of very intense short radio bursts from Neptune was possible as early as 30 days before closest approach and at least 22 days after closest approach. The bursts lay at frequencies in the range 100 to 1300 kilohertz, were narrowband and strongly polarized, and presumably originated in southern polar regions ofthe planet. Episodes of smooth emissions in the frequency range from 20 to 865 kilohertz were detected during an interval of at least 10 days around closest approach. The bursts and the smooth emissions can be described in terms of rotation in a period of 16.11 +/- 0.05 hours. The bursts came at regular intervals throughout the encounter, including episodes both before and after closest approach. The smooth emissions showed a half-cycle phase shift between the five episodes before and after closest approach. This experiment detected the foreshock of Neptune's magnetosphere and the impacts of dust at the times of ring-plane crossings and also near the time of closest approach. Finally, there is no evidence for Neptunian electrostatic discharges.