Identifying and quantifying the different drivers of energy ﬂow through a planetarymagnetosphere is crucial for understanding how each planetary system works. The magnetosphere of ourown planet is primarily driven externally by the solar wind through global magnetic reconnection, while aviscous-like interaction with the solar wind involving growth of the Kelvin-Helmholtz (K-H) instability is asecondary effect. Here we consider the solar wind-magnetosphere interaction at all magnetized planets,exploring the implications of diverse solar wind conditions. We show that with increasing distance fromthe Sun the electric ﬁelds arising from reconnection at the magnetopause boundary of a planetarymagnetosphere become weaker, whereas the boundaries become increasingly K-H unstable. Our resultssupport the possibility of a predominantly viscous-like interaction between the solar wind and every oneof the giant planet magnetospheres, as proposed by previous authors and in contrast with the solarwind-magnetosphere interaction at Earth.