Investigating Charon’s Impact on Pluto’s Interaction with the Solar Wind through Multifluid MHD Simulations

Abstract:

Charon’s mass, orbital parameters, and distinct surface composition relative to Pluto suggest that it plays a significant role in Pluto’s dynamic interaction with the solar wind. Its high mass ( ~ 10% of total system mass ) and close orbit ( < 20 Pluto Radii ) are thought to result in regionally enhanced atmospheric escape from Pluto as well as ionospheric deformation. Additionally, there are multiple mechanisms through which Charon could possess a tenuous atmosphere—and therefore ionosphere. Firstly, spectral observations of short-lived hydrated ammonia on Charon’s surface could be caused by semi-regular cryovolcanism, which would also source a water group atmosphere (Cook et al., 2007). Secondly, recent work indicates that Charon could have a nightside parasitic atmosphere that is captured from material escaping from Pluto (Tucker et al., 2014). Either possibility would result in Charon presenting a sizable obstacle to the incoming solar wind. This work studies Charon’s effects on the Pluto-solar wind interaction using a 3-dimensional multifluid MHD model which has been modified to include a second body within the system. This second body (Charon) represents not only an additional gravitational perturbation to the system, but can also provide a local and distinct plasma source, a sink for plasma sourced from Pluto or the solar wind, and cause an obstruction and perturbation to the solar wind. Specifically, we investigate the possibility of enhanced ionospheric loss from Pluto due to Charon’s gravitational attraction, as well as the overall dynamics of a two-body system interacting with the solar wind in which each body has an ionosphere and periodically passes through the bow shock of the other body. The former objective is made possible by tracking the flux of plasma sourced from Pluto. The latter objective is accomplished by performing simulations in which Charon is upstream of Pluto as well as simulations in which Charon is placed downstream, within Pluto's wake.