Heliospheric Variation In Response To Changing Interstellar Environments

While unchanging on human timescales, the interstellar environment has been and will be very different from current conditions. Historically, the heliosphere and solar system have been in regions of the galaxy that were much hotter, or contained higher concentrations of neutral hydrogen, or with interstellar clouds with higher or lower speeds, than is the case today. In this chapter, we describe the response of the heliosphere to different interstellar environments, taking into account the basic physics of the coupled neutral hydrogen and plasma self-consistently.