IBEX's Enigmatic Ribbon in the sky and its many possible sources

Launched in October 2008, NASA's Interstellar Boundary Explorer (IBEX) has provided the first-ever energy-resolved all-sky maps of energetic neutral atom (ENA) emissions from the boundary of the heliosphere with the local interstellar medium (LISM). The maps reveal an enigmatic "Ribbon" of enhanced emissions superposed on a smoothly varying global distribution of ENA emissions. The Ribbon lies between the locations where the two Voyagers crossed the termination shock and was not sampled by them on their trajectories out through the heliosphere. IBEX's discovery of the Ribbon-a feature completely unpredicted by theory and numerical simulations-requires a new paradigm in our understanding of the heliosphere/LISM interaction. The Ribbon appears to be ordered by the interstellar magnetic field and the solar wind's latitudinal structure. The Ribbon's origin, whether from processes occurring in the heliosphere or beyond in the LISM, is unknown and the subject of intense investigation. Continued observations over the first 3 years of the IBEX mission have characterized the Ribbon, including its location, energy spectra, fine structure, and time variations.