| As the spacecraft New Horizons makes its journey toward Pluto and beyond, the Solar Wind Around Pluto (SWAP) instrument collects energy spectra of the solar wind and interstellar pick-up ions (PUIs), which are interstellar neutral particles that have been ionized and picked-up by the solar wind's motional electric field. For this dissertation, working with several co-authors, I performed analysis of this data and of the SWAP instrument itself. First, we analyzed SWAP data taken between 11 and 12 AU and found a correlation between the number density of PUIs and solar wind protons. Then, we were able to fit an isotropic PUI model to a previously reported special SWAP measurement taken at 11.3 AU of unexpectedly anisotropic PUIs, as well as to a similar SWAP measurement taken at 17 AU. Finally, we analyzed SWAP data taken between 11 and 22 AU to characterize PUI properties in the outer heliosphere, where essentially no PUIs had been previously measured. Through simulations of the SWAP instrument, we discovered a previously unaccounted-for energy dependence of the instrument's geometric factor, a result that accounted for the apparent anisotropic PUI distributions measured by SWAP. Also, through simulations and detailed calibration of the SWAP flight spare in the laboratory, we showed that particles from the measured distribution reflect from the walls of the instrument to produce an important background at energies around and far below that of the primary distribution; this discovery could be important for design and analysis of data from some space plasma instruments. |
