"Astronomy with Neutral Atoms: IBEX Catches the Interstellar Wind and Probes the Heliospheric Boundary"

Abstract: 400 years after Galileo pointed a telescope at celestial objects for the first time, we have now added neutral atoms to our astronomical toolbox with the Interstellar Boundary Explorer (IBEX), which was launched October 19, 2008. Since early 2009, two energetic neutral atom (ENA) cameras take global images of the interaction of the solar system with its neighborhood. The IBEX-Lo camera catches the interstellar wind of neutral H, He, O, and Ne atoms that blows through the solar system with a speed of ≈23 km/s and arises from the Sun’s motion through the neighboring interstellar gas cloud. This interstellar gas flow provides us with an excellent probe of the state of the local interstellar cloud and of its interaction with the heliospheric boundary region. The deduced neutral interstellar flow vector puts us right into the local interstellar cloud. Both IBEX cameras have returned stunning images of the heliospheric boundary region, where the solar wind slows down in response to the surrounding interstellar medium. The images show an unexpected bright “Ribbon” across the sky, which provides us with a marker for the direction of the interstellar magnetic field, but the processes leading to the bright ENA emission are not yet understood. The IBEX results are about to revolutionize our understanding of the Sun’s interaction with its galactic neighborhood.