Solar-wind control of the extent of planetary ionospheres

In our solar system there are at least four magnetic planets: Earth, Jupiter, Mercury, and Mars; while at least one planet, Venus, appears to be essentially nonmagnetic. The ionospheres of the magnetic planets are imbedded in their magnetosphere and thus shielded from the solar wind, whereas the ionosphere of Venus, at least, interacts directly with the solar wind. However, the solar wind interaction with the planetary environment, in both cases, affects the behavior of their ionospheres. The role the solar wind interaction plays in limiting the extent of the ionospheres of both magnetic and nonmagnetic planets is discussed.