Interactions with planetary ionospheres and atmospheres - A review

The interaction of the solar wind with unmagnetized objects possessing an ionosphere is reviewed, with emphasis on recent developments. Venus, Mars, Titan, comets (including the artificial comet created by AMPTE) and the unusual interplanetary events interpreted as cometesimals are considered. The role of the interplanetary magnetic field and of mass loading in producing the observed interactions are highlighted. Interpretation to date is based largely on an MHD (fluid) treatment, but recent results from the first AMPTE barium release and from recordings made at Venus suggest that finite Larmor radius effects introduce asymmetries in the solar wind interaction.