2015ApJ...801...61F

The journey of the Sun through space carries the solar system through a dynamic interstellar environment that is presently characterized by a Mach ∼1 motion between the heliosphere and the surrounding warm partially ionized interstellar cloud. The interaction between the heliosphere and interstellar medium is an evolving process due to variable solar wind properties and the turbulent nature of the interstellar cloud that surrounds the heliosphere. Frisch et al. presented a meta-analysis of the historical data on the interstellar wind flowing through the heliosphere and concluded that temporal changes in the ecliptic longitude of the flow direction with time were statistically indicated by the data available in the refereed literature at the time of that writing. Lallement & Bertaux disagree with this result, and suggested, for instance, that a key instrumental response function of IBEX-Lo was incorrect and that the STEREO pickup ion data are unsuitable for diagnosing the flow of interstellar neutrals through the heliosphere. In this paper we first show that temporal variations in the interstellar wind through the heliosphere are consistent with our knowledge of the very local interstellar medium. The statistical analysis of the helium wind data is revisited, and a recent correction of a typographical error in the literature is incorporated into the new fits. With this correction, and including no newer IBEX results, these combined data still indicate that a change in the longitude of the interstellar neutral wind of λ = 5.°6±2.°4 over the past forty years remains statistically likely, but an constant flow longitude is now statistically possible. Other scenarios for the selection of subsets of these data used in the fitting process produce similar conclusions. We show that the speculations made by Lallement & Bertin about the IBEX instrumental response function are incorrect, and that their other objections to the data used in the meta-analysis are either incorrect or unproven. Further investigations of the historical interstellar wind data and continuing analysis of additional IBEX data may provide a more definitive result on the stability of the flow of interstellar gas through the heliosphere.