OXYGEN OUTFLOW IN THE MARTIAN MAGNETOTAIL

Characteristic features of the oxygen ion (O+) outflow in the nightsid e of Mars. have been studied. The data set used includes all high tele metry O+ energy spectra observations made by the ASPERA particle instr ument onboard the Phobos 2 spacecraft. Oxygen outflow within the optic al shadow of Mars was detected on all orbits, but no clear structure w as found when the ions were organised according to the cross-flow comp onent of the interplanetary magnetic field (IMF). Oxygen ions in the t ail outside the shadow were, in contrast, detected only on a few orbit s and were related to fluctuating magnetosheath magnetic and electric fields with non-Parker spiral IMF orientation. The analysis indicates that O+ ions within the optical shadow from a ''steady'', ever persist ing outflow feature. The high energy O+ ions in the tail outside the o ptical shadow are in contrast possibly a manifestation of the dynamic nature of the Martian tail, although effects associated to an asymmetr ic tail can not be fully excluded.