Testing the Interstellar Wind Helium Flow Direction with Galileo Euvs Data

Monday, 15 December 2014
Wayne Robert Pryor1, Karen E Simmons2, Joseph M Ajello3, W Kent Tobiska4, Kurt D Retherford5, S Alan Stern6, Paul D Feldman7, Priscilla C Frisch8, Maciej Bzowski9 and Cesare Grava6, (1)Central Arizona College, Coolidge, AZ, United States, (2)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (3)Jet Propulsion Laboratory, Pasadena, CA, United States, (4)Space Environment Technologies, Pacific Palisades, CA, United States, (5)Southwest Research Inst, San Antonio, TX, United States, (6)Southwest Research Institute San Antonio, Space Sci & Engineering Div, San Antonio, TX, United States, (7)Johns Hopkins Univ, Baltimore, MD, United States, (8)University of Chicago, Chicago, IL, United States, (9)Space Research Center Polish Academy of Sciences, Warsaw, Poland
Forty years of measurements of the flow of interstellar helium through the heliosphere suggest that variations of the flow direction with time are possible. We will model Galileo Extreme Ultraviolet Spectrometer (EUVS) data to determine the best-fitting flow direction and compare it to values obtained by other spacecraft. The Galileo EUVS (Hord et al., 1992) was mounted on the spinning part of the spacecraft and obtained interstellar wind hydrogen Lyman-alpha 121.6 nm and helium 58.4 nm data on great circles passing near the ecliptic poles during the interplanetary cruise phase of the mission and also during the Jupiter orbital phase of the mission. The Galileo hydrogen cruise data have been previously published (Hord et al., 1991, Pryor et al., 1992; 1996; 2001), but the helium data have not. Our model was previously used by Ajello et al., 1978, 1979 to model Mariner 10 interstellar wind helium data, and by Stern et al., 2012 and Feldman et al., 2012 to model the interplanetary helium background near the moon in Lunar Reconnaissance Orbiter (LRO) Lyman-alpha Mapping Project (LAMP) data. The model has been updated to include recent determinations of daily helium 58.4 nm solar flux variations and helium losses due to EUV photoionization and electron impact ionization.