Date of Award
Doctor of Philosophy (PhD)
Interstellar matter., Heliosphere (Astrophysics), Solar wind.
The heliosphere is a “comet-like” bubble of plasma reaching from &sim102 to over 103 astronomical units in size. It is created by the outflow of solar wind (SW) plasma and its interaction with the partially-ionized local interstellar medium (LISM). Due to its large size, it is unfeasible to take in situ measurements at the edges of this interaction. Therefore it is necessary to develop sensing techniques to remotely probe the heliosphere and its boundaries. The NASA-funded Interstellar Boundary EXplorer (IBEX) mission is aimed at improving our understanding of the heliospheric interface. Launched in 2008 October, IBEX measures fluxes of energetic neutral atoms (ENAs) that are created through the SW–LISM interaction, as well as interstellar neutral atoms that permeate the heliospheric boundary. Out of the neutral atom species that IBEX can detect, hydrogen (H) atoms are the most abundant in interstellar space and the heliosphere. Hydrogen ENAs, in particular, are created when relatively energetic protons from the heliospheric plasma charge-exchange with interstellar H atoms. Due to their high energies, and thus large mean free paths, H ENAs can propagate large distances before ionizing (i.e., on the order of the size of the heliosphere), and can be detected by IBEX. The purpose of this study is to simulate H ENA flux measurements at 1 AU and relate these to the IBEX mission. Three goals of this study that are of particular interest to IBEX are: (1) to simulate H ENA fluxes measured in the solar (inertial) and IBEX spacecraft frames of reference in order to better understand IBEX measurements made in different frames of reference; (2) to study the effects of pickup ions, i.e., non-thermalized ions, on H ENA fluxes, and determine how IBEX observations can reveal the properties of PUIs in the distant heliosphere; (3) to analyze the effects of a time-dependent solar cycle on IBEX H ENA measurements, particularly the “ribbon” of enhanced flux encircling the sky. The simulations are performed by post-processing a pre-simulated, “background” heliosphere containing plasma and neutral H properties (e.g., density, temperature, velocity) produced from a three-dimensional magnetohydrodynamic/kinetic simulation of the SW–LISM interaction.
Zirnstein, Eric J., "Simulating hydrogen energetic neutral atom flux measurements for NASA's IBEX mission" (2014). Dissertations. 57.