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We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV) H, O, and S ions from the region of the IPT seems to be the likely source of the X-ray emission from the Galilean satellites. According to our estimates, fluorescent X-ray emission excited by solar X-rays, even during flares from the active Sun, charge-exchange processes, previously invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains fail to account for the observed emission. On the other hand, bremsstrahlung emission of soft X-rays from nonthermal electrons in the few hundred to few thousand eV range may account for a substantial fraction of the observed X-ray flux from the IPT.

Cloud‐tracked wind observations document the role of eddies in putting momentum into the zonal jets. Chemical tracers, lightning, clouds, and temperature anomalies document the rising and sinking in the belts and zones, but questions remain about what drives the flow between the belts and zones. We suggest an additional role for the eddies, which is to generate waves that propagate both up and down from the cloud layer. When the waves break they deposit momentum and thereby replace the friction forces at solid boundaries that enable overturning circulations on terrestrial planets. By depositing momentum of one sign within the cloud layer and momentum of the opposite sign above and below the clouds, the eddies maintain all components of the circulation, including the stacked, oppositely rotating cells between each belt‐zone pair, and the zonal jets themselves. The dark belts and bright zones that circle the planet at constant latitude, along with the jet streams on the belt‐zone boundaries, are the iconic dynamical features of Jupiter's atmosphere. But the circulation cells with rising, sinking, and cross‐latitude motion are just as important because they maintain the storms and turbulent eddies. Voyager and Cassini have shown that the turbulent eddies put energy into the jet streams. We argue that the eddies also put energy into the circulation cells. They do this by generating waves that break as they propagate above and below the clouds. The breaking waves provide the essential forces that replace those that occur on planets with solid boundaries. This study proposes a dynamical mechanism that maintains the circulation cells connecting neighboring belts and zones of JupiterWaves that propagate down from the cloud layer are key; when they break they produce a drag force that mimics the effect of a solid boundaryEddies within the clouds drive the zonal jets and probably drive the waves, thereby driving all aspects of the zonal mean circulation This study proposes a dynamical mechanism that maintains the circulation cells connecting neighboring belts and zones of Jupiter Waves that propagate down from the cloud layer are key; when they break they produce a drag force that mimics the effect of a solid boundary Eddies within the clouds drive the zonal jets and probably drive the waves, thereby driving all aspects of the zonal mean circulation