Wednesday

How the outer planet magnetospheres evolve after the Sun turns off of the main sequence has relevant applications for extrasolar planetary systems. Here we determine how the size of planetary magnetospheres evolve over time from the end of the main sequence through to the white dwarf phase due to the violent winds of red giant and asymptotic giant branch stars. By using a rough semianalytic prescription, we investigate the entire relevant phase space of planet type, planet orbit and stellar host mass. We find that the planetary magnetosphere will always be quashed at some point during the giant branch phases unless the planet’s magnetic field strength is at least two orders of magnitude higher than Jupiter’s current value. We also show that the time variation of the stellar wind and density does not allow a magnetosphere to be maintained at any time for field strengths less than 10^(−5) T (0.1 G). This lack of protection hints that the outer planets in the solar system and similar planets in extrasolar systems will lose their magnetospheres multiple times before the white dwarf stage of stellar evolution.