Breaking Correlation in the Inflow Parameters of Interstellar Neutral Gas in Direct-sampling Observations

Abstract

Abstract We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyses of observations performed by an onboard Interstellar Boundary Explorer (IBEX) instrument, IBEX-Lo. We point out that this correlation is the combined result of the inability to measure the speed of the atoms that enter the instrument and the restriction of the observations to a short orbital arc around the Sun performed by the instrument during observation. We demonstrate that without the capability to measure the speed, but with the ability to perform observations along longer orbital arcs, or from at least two distant locations on the orbit around the Sun, it is possible to break the parameter correlation. This, however, requires the capability of adjusting the boresight of the instrument relative to the spacecraft rotation axis, such as that of the planned camera on board the Interstellar Mapping and Acceleration Probe (IMAP), IMAP-Lo.