The bow shocks and upstream waves of Venus and Mars Original Research Article

Because they both lack measurable magnetic fields, Venus and Mars are often compared to each other in terms of their solar wind interaction. Upstream from each planet the most distant signs of this interaction occur at the bow shock, and in regions upstream from the shock where plasma waves are observed. In many respects the collisionless shocks at Venus and Mars are quite different. The Martian shock is located slightly farther from the planet (with respect to planetary size) and is more variable than the Venus shock. In addition, the position of the Martian shock is not observed to correlate strongly with solar cycle, unlike at Venus. These differences indicate that the solar wind obstacles at the two planets are somehow quite different. However, the characteristics of observed upstream waves at the two planets (and at other solar system bodies) suggest that similar processes are at work at both shocks, and that the size and shape of the shock do not play significant roles in wave generation or damping. This review compares the observations of the bow shocks and upstream waves at Venus and Mars, with reference to model predictions and observations at Mercury and Earth.