Interaction of a Magnetized Plasma With an Unmagnetized Planet: A Tale of Two Spacecraft

While many spacecraft have explored Venus and its solar wind interaction, much of our understanding is based on the observations from two well instrumented long-lived orbiters. Pioneer Venus has told us much of what we know under solar maximum conditions while Venus Express has provided complementary data at solar minimum. The pressure of the cold ionospheric plasma and its embedded magnetic field stands off the dynamic pressure of the solar wind. At solar maximum the pressure balance point is generally at high altitudes where the plasma is collisionless and the dayside ionosphere stays field-free except when the dynamic pressure is high. At solar minimum the ionospheric pressure stands off the solar wind at lower altitudes where the plasma is collisional. This allows faster diffusion of magnetic field into the ionosphere and it becomes more fully magnetized. Herein, we review our present understanding of the solar wind interaction with Venus based on these observations together with global MHD simulations.