WAVE ACTIVITY NEAR PLUTO

In this paper, we analyze wave activity near Pluto. The situation is s omewhat analogous to that near comets: molecules (in this case methane ) escape from the atmosphere; some are phono-ionized, and a comet-like mass-loading of the solar wind plasma takes place. But the wave activ ity due to planetary ion interaction with the solar wind is quite diff erent from that near comets. In the weak interplanetary magnetic field near Pluto, there is no MHD wave excitation; instead, we show that io n acoustic waves are excited. We construct a nonlinear theory of ion-a coustic wave excitation. These waves are excited due to a dissipative instability. The frequency, characteristic growth rate, and spatial sc ale of the instability are calculated. The main physical mechanism for wave amplitude saturation is the smearing of the velocity distributio n function of the beam ions. We use a quasilinear approach to determin e the characteristic scale for the electric wave amplitude.