We present analyses from the five Pioneer Venus Orbiter plasma experim
ents and the plasma wave experiment when a patch of plasma with enhanc
ed densities was encountered in the near-Venus ionotail during atmosph
eric entry at an altitude of similar to 1100 km in the nightside ionos
phere. Our analyses of the thermal and superthermal ion measurements i
n this plasma feature provides the first evidence that at times molecu
lar ions in the 28-32 amu mass range are dominant over atomic mass spe
cies thus yielding evidence for a transport mechanism that reaches int
o the lower ionosphere. Analysis of plasma analyzer (OPA) observations
at this time indicates the presence of ions measured in the rest fram
e of the spacecraft at similar to 27 and 37 volt energy per unit charg
e steps. In the rest frame of the planet these superthermal ions are f
lowing from the dawn direction at speeds (assuming they are O-2(+)) of
similar to 8 km/s and with a flow component downward (perpendicular t
o the ecliptic plane) at speeds of similar to 2 km/s. OPA analyses als
o determine the ion number flux, energy, flow angles, and angular dist
ributions. Plasma wave bursts appear to indicate that plasma density d
ecreases within and on the equatorward edge of the patch of enhanced p
lasma densities are associated with ion acoustic waves and relative io
n streaming.