Nonlinear evolution of modified two‐stream instability above ionosphere of Titan: Comparison with the data of the Cassini Plasma Spectrometer

Abstract

The ionosphere of Titan, moon of Saturn, is directly exposed to the streaming plasma either of magnetospheric or solar wind origin. A turbulent interaction region is formed, called here flowside plasma mantle, where both cold ionospheric and hot streaming plasma are present at comparable densities. Within the framework of a one‐dimensional electromagnetic hybrid simulation using realistic electron mass we have shown that significant wave activity may be generated because of a modified two‐stream instability (MTSI). Having its free energy in the relative drift between the streaming ion flow and the ionospheric ions MTSI is very effective in generating “anomalous viscosity” type interaction leading to significant bulk velocity loss of the proton component of the external plasma flow and turbulent heating of the ionospheric ions. The stochastic energy transfer from the streaming plasma to the ionospheric ions may also increase the tailward planetary ion escape by collective pickup mechanism enhancing the rate of erosion of the atmosphere of Titan. We predict significant wave activity within the characteristic frequency range of about 1–10 Hz and at saturated wave electric field levels of about 5–25 mV/m. Similarly, according to our model calculations superthermal charged particles of ionospheric origin with kinetic energies of about few tens of eV are expected to be detectable by the charged particle analyzers onboard of Cassini spacecraft close to the upper edge of Titan's ionosphere.