Venus/Mars pickup ions and ionosheath wave structures Original Research Article

A search for ULF waves associated with pickup ions was undertaken for Venus and for Mars. The Pioneer Venus Orbital Plasma Analyzer (OPA) measurements of ion energy per unit charge spectra provided signatures of the probable presence of pick-up ions. At the locations of these energetic ion signatures we derived power spectra and propagation characteristics of structures in the local magnetic field from measurements by the Pioneer Venus Orbiter Magnetometer. Some of these features are characteristic of effects previously identified in the ionosheath of Venus, analogous to wave activity properties in the Earth’s magnetosheath. However, for the first time examples have been found at Venus of ULF waves near the ion gyrofrequencies in the ionosheath and in the far magnetic tail. Both linear and elliptically polarized waves are found in the vicinity of ion pickup detections. The signatures of these features are presented using one orbit of Pioneer Venus Orbiter data. The same wave analysis techniques are applied to the magnetic field data measured on one characteristic orbit from the Mars Global Surveyor Magnetometer. This is used to demonstrate how a comparative analysis of the two planets can be useful.