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Neutral Interstellar Helium (NISHe) is almost unaffected at the heliosphericinterface with the interstellar medium and freely enters the solar system. Itprovides some of the best information on the characteristics of theinterstellar gas in the Local Interstellar Cloud. The Interstellar BoundaryExplorer (IBEX) is the second mission to directly detect NISHe. We present acomparison between recent IBEX NISHe observations and simulations carried outusing a well-tested quantitative simulation code. Simulation and observationresults compare well for times when measured fluxes are dominated by NISHe (andcontributions from other species are small). Differences between simulationsand observations indicate a previously undetected secondary population ofneutral helium, likely produced by interaction of interstellar helium withplasma in the outer heliosheath. Interstellar neutral parameters arestatistically different from previous in situ results obtained mostly from theGAS/Ulysses experiment, but they do agree with the local interstellar flowvector obtained from studies of interstellar absorption: the newly-establishedflow direction is ecliptic longitude 79.2 deg, latitude -5.1 deg, the velocityis \sim 22.8 km/s, and the temperature is 6200 K. These new results imply amarkedly lower absolute velocity of the gas and thus significantly lowerdynamic pressure on the boundaries of the heliosphere and different orientationof the Hydrogen Deflection Plane compared to prior results from Ulysses. Adifferent orientation of this plane also suggests a new geometry of theinterstellar magnetic field and the lower dynamic pressure calls for acompensation by other components of the pressure balance, most likely a higherdensity of interstellar plasma and strength of interstellar magnetic field.

Neutral interstellar helium parameters based on IBEX-Lo observations and test particle calculations