Investigating Pickup Ions with New Horizons, Ulysses and Voyager and Their Diagnostics By Fluxes of Energetic Neutral Atoms

Abstract:

Pickup ions (PUIs) play a major role in the solar wind (SW) interaction with the local inter-
stellar medium (LISM). An understanding of the transport of PUIs in the heliosphere is important.
Here, we solve the transport equation to examine the detailed spatial evolution of the PUI distri-
bution in supersonic solar wind. The effects of second-order Fermi process, i.e. velocity diffusion,
convection with the solar wind, adiabatic cooling and continual injection of newly born PUIs are
all included. We analyze the transition of PUIs at the heliospheric termination shock (TS) and
describe the heliosheath PUI distribution taking into account ongoing velocity diffusion. A three-
dimensional, MHD-kinetic model for flows of a thermal plasma, neutral atoms and PUIs has been
developed. The flow of the plasma is modeled using solutions to MHD equations. The PUI transport
module analyzes the spatial variation of the PUI distribution function as a separate component, on
a kinetic level. We perform a comparison of our numerical results with observations made by New
Horizons, Ulysses and Voyager. Fluxes of energetic neutral atoms (ENA) with energies of about
0.2-6 keV originating through charge exchange of H atoms with the compressed solar wind and
with PUIs behind the TS and arriving at 1 AU are calculated. Our results are directly comparable
with the actual IBEX distributed ENA sky maps. A comparison of our numerical results with
measurements performed by IBEX will allow us to answer the challenging question: how the PUI
distribution affects the ENA fluxes from the heliosheath?