Wave generation in moon–satellite interactions

Abstract

The regions in space plasmas where mass loading occurs are rich environments for the generation of low frequency waves. We discuss wave generation in the interaction regions of Io and Europa with Jupiter's magnetosphere. We contrast processes in these regions with wave generation near comets. Mass loading occurs when neutrals from Io exosphere are ionized and picked up into the plasma torus. Pickup ions have ring distributions able to generate waves. Galileo data showed the existence of ion cyclotron waves in the Io torus with frequencies near the gyrofrequencies of SO 2 +, SO +, and S + ions. Wave location suggests a fan-shaped region of ion pickup extending downstream from Io. In addition, mirror mode waves have been observed in Io's wake. At Europa the mass loaded into the magnetosphere is less than from Io. Galileo observed transverse waves in the wake with frequencies near the gyrofrequencies of O 2 +, and Cl + ions. Wave characteristics indicate that they are ion cyclotron waves generated by pickup ions. Wave power suggests that the pickup ion rate is larger when Europa is near the center of the jovian current sheet than when the moon is outside of it. The dominant mode near these satellites depends on pickup ion composition. Wave properties are not uniform indicating that the spatial distribution of pickup ions is not homogeneous. Wave generation near comets occurs because cometary material is ionized and picked up into the solar wind. The nature of the interaction region and of pickup ions is determined by solar wind properties and the gas production rate of the comet. In contrast to moon–satellite interactions, in this case pickup ions can have a significant parallel drift velocity and more wave modes are unstable. Waves near comets include, H 2O + ion cyclotron waves, magnetosonic/whistler waves, and mirror mode.