RADIO-FREQUENCY SIGNALS IN JUPITER ATMOSPHERE

During the Galileo probe's descent through Jupiter's atmosphere, under the ionosphere, the lightning and radio emission detector measured ra dio frequency signals at levels significantly above the probe's electr omagnetic noise. The signal strengths at 3 and 15 kilohertz were relat ively large at the beginning oi the descent, decreased with depth to a pressure level of about 5 bars, and then Increased slowly until the e nd of the mission. The 15-kilohertz signals show arrival direction ani sotropies. Measurements of radio frequency wave forms show that the pr obe passed through an atmospheric region that did not support lightnin g within at least 100 kilometers and more likely a few thousand kilome ters of the descent trajectory. The apparent opacity of the jovian atm osphere increases sharply at pressures greater than about 4 bars.