Space Science Reviews

, Volume 146, Issue 1, pp 149-172

First online:

Diagnosing the Neutral Interstellar Gas Flow at 1 AU with IBEX-Lo

  • E. MöbiusAffiliated withSpace Science Center & Department of Physics, University of New Hampshire Email author 
  • , H. KucharekAffiliated withSpace Science Center & Department of Physics, University of New Hampshire
  • , G. ClarkAffiliated withSpace Science Center & Department of Physics, University of New Hampshire
  • , M. O’NeillAffiliated withSpace Science Center & Department of Physics, University of New Hampshire
  • , L. PetersenAffiliated withSpace Science Center & Department of Physics, University of New Hampshire
  • , M. BzowskiAffiliated withSpace Research Centre, Polish Academy of Sciences
  • , L. SaulAffiliated withPhysikalisches Institut, Universität Bern
  • , P. WurzAffiliated withPhysikalisches Institut, Universität Bern
  • , S. A. FuselierAffiliated withLockheed Martin Advanced Technology Lab
    • , V. V. IzmodenovAffiliated withMoscow State University and Space Research Institute, Russian Academy of Sciences
    • , D. J. McComasAffiliated withSouthwest Research Institute
    • , H. R. MüllerAffiliated withDepartment of Physics and Astronomy, Dartmouth College
    • , D. B. AlexashovAffiliated withSpace Research Institute (IKI) and Institute for Problems in Mechanics, Russian Academy of Sciences

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Every year in fall and spring the Interstellar Boundary Explorer (IBEX) will observe directly the interstellar gas flow at 1 AU over periods of several months. The IBEX-Lo sensor employs a powerful triple time-of-flight mass spectrometer. It can distinguish and image the O and He flow distributions in the northern fall and spring, making use of sensor viewing perpendicular to the Sun-pointing spin axis. To effectively image the narrow flow distributions IBEX-Lo has a high angular resolution quadrant in its collimator. This quadrant is employed selectively for the interstellar gas flow viewing in the spring by electrostatically shutting off the remainder of the aperture. The operational scenarios, the expected data, and the necessary modeling to extract the interstellar parameters and the conditions in the heliospheric boundary are described.

The combination of two key interstellar species will facilitate a direct comparison of the pristine interstellar flow, represented by He, which has not been altered in the heliospheric boundary region, with a flow that is processed in the outer heliosheath, represented by O. The O flow distribution consists of a depleted pristine component and decelerated and heated neutrals. Extracting the latter so-called secondary component of interstellar neutrals will provide quantitative constraints for several important parameters of the heliosheath interaction in current global heliospheric models. Finding the fraction and width of the secondary component yields an independent value for the global filtration factor of species, such as O and H. Thus far filtration can only be inferred, barring observations in the local interstellar cloud proper. The direction of the secondary component will provide independent information on the interstellar magnetic field strength and orientation, which has been inferred from SOHO SWAN Ly-α backscattering observations and the two Voyager crossings of the termination shock.


Interstellar gas Heliosphere Instrumentation