Venus Tail Research Articles

Wave‐particle interactions in the Venus wake and tail

We present the first analysis of Pioneer Venus Orbiter plasma, electric field, and magnetic field observations in the Venus tail. We have studied the first season of Pioneer Venus Orbiter tail passage (approximately June 1979) in order to determine the main plasma and field configuration in this region at this time and to ascertain some of the basic physical processes. Our analysis shows that the boundary of the Venusian tail is often characterized by changing plasma distributions and enhanced plasma wave activity. We use summary plasma probe parameters to argue that the waves are Doppler‐shifted ion acoustic oscillations. In the magnetotail region there is generally an exclusion of high‐density plasma, but when plasma is detected, the distributions often appear to be non‐Maxwellian at the highest time resolution, and these distorted distribution functions are generally accompanied by enhanced plasma wave signals and magnetic field reversals indicative of electric currents. On the basis of our analyses of the high‐resolution plasma and wave observations for orbit 189, we identify a different time from that previously defined on the basis of the magnetic field data for the spacecraft entrance into the magnetotail. The wave activity in the Venus tail appears similar to the broadband noise identified in the earth's tail, but at Venus the levels are usually higher.

Venus nightside ionospheric holes: The signatures of parallel electric field acceleration regions?

Recent observations by the instruments onboard the Pioneer Venus spacecraft have revealed the existence of "holes" or regions of density depletion in the nightside Venus ionosphere associated with regions of radial magnetic fields. The properties of the electrons within the core of these holes are suggestive of an acceleration process along the magnetic field lines as are the Venera 9 and 10 observations of energetic ions in the Venus tail. Given the observational information, we attribute these Venusian plasma depletions to the presence of parallel electric fields similar to those observed in the terrestrial auroral ionosphere. The resulting electric field accelerates electrons down the field lines producing heating of the depleted thermal electron population within the hole and production of ionization below the hole. Simultaneously ionospheric ions are accelerated outward toward the plasmasheet.