Pluto's ionospheric models and solar wind interaction

Chemical model calculations are carried out to describe the ion composition and density profile of Pluto's ionosphere. With the adopted surface pressure (≈ 10 microbars) of the N 2 gas and the mixing ratio of CH 4 (≈7.4×10 −3), the major ion is found to be H 2CN + and the peak ion number density is estimated to be about 3×10 3 cm −3. If Pluto does not have an intrinsic magnetic field, the ionospheric penetration of the interplanetary magnetic field and solar wind plasma would be stopped at an altitude of about 1400 km because of collisional friction of the neutral atmosphere.