Ion Temperature Anisotropies in the Venus Plasma Environment

Abstract: Velocity distributions are a key to understanding the interplay between particles and waves in a plasma. Any deviation from a Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer MAG on-board Venus Express,  ion distributions in the plasma environment of Venus are studied. The focus lies on temperature anisotropy, that is, the difference between the ion temperature parallel and perpendicular to the background magnetic field. This study presents spatial maps of the average ratio between the perpendicular temperature  and parallel temperature , both for proton and heavy ions (atomic oxygen, molecularoxygen and carbon dioxide). Furthermore average values of  and  are calculated for different spatial areas around Venus. The results show that proton  and  are nearly equal in the solar wind. At the bow shock and in the magnetosheath, the ratio  increases to provide conditions favoring mirror mode wave generation. An even higher anisotropy is found in the magnetotail with  for both protons and heavy ions.