The Interstellar Boundary Explorer (IBEX): Tracing the Interaction
  between the Heliosphere and Surrounding Interstellar Material with Energetic
  Neutral Atoms
  The Interstellar Boundary Explorer (IBEX) mission is exploring the frontiers
of the heliosphere where energetic neutral atoms (ENAs) are formed from charge
exchange between interstellar neutral hydrogen atoms and solar wind ions and
pickup ions. The geography of this frontier is dominated by an unexpected
nearly complete arc of ENA emission, now known as the IBEX 'Ribbon'. While
there is no consensus agreement on the Ribbon formation mechanism, it seems
certain this feature is seen for sightlines that are perpendicular to the
interstellar magnetic field as it drapes over the heliosphere. At the lowest
energies, IBEX also measures the flow of interstellar H, He, and O atoms
through the inner heliosphere. The asymmetric oxygen profile suggests that a
secondary flow of oxygen is present, such as would be expected if some fraction
of oxygen is lost through charge exchange in the heliosheath regions. The
detailed spectra characterized by the ENAs provide time-tagged samples of the
energy distributions of the underlying ion distributions, and provide a wealth
of information about the outer heliosphere regions, and beyond.
