Bi-ion structuring in the magnetosheath of Mars: Theoretical modeling

Mars gives us an example of a planetary mngnetosheath region which is decisively determined by the interaction of the solar wind with the heavy ion plasma of planetary/exospheric origin. Another important feature of the Martian plasma environment is that the characteristic extension of the magnetosheath is less than the pick-up gyroradius. In such Large Larmor Radius systems a relative streaming of different ion species is admissible and introduces a strong coupling between protons and planetary ions. As seen in our 2D bi-ion MHD model, this coupling causes many interesting new effects. in addition to the ion composition boundary (protonopause) a shock-like transition is formed in the low-dense heavy ion flow downstream of the proton bow shock. This so-called heavy ion discontinuity (HID) represents the outer boundary of a region where heavies and protons have nearly equal mass densities and owing to intense coupling between both flows, multiple bi-ion discontinuities (with a ray structure) are produced. These features are basically confirmed by comparison with the plasma observations made on the Phobos-2 spacecraft. It also offers a way for a better understanding of similar structures near comets, Venus and AMPTE releases. (C) 1997 COSPAR. Published by Elsevier Science Ltd.