Energetic Neutral atoms, IBEX, and the “Ribbon”

By Thomas Ostrander, Dr. Jacob Heerikuisen, And Eric Zirnstein2

December 2, 2013

Abstract

When it was launched in late 2008 the Interstellar Boundary EXplorer (IBEX) was intended to map the numbers and energies of Energetic Neutral Atoms (ENAs) of hydrogen coming in from the outer solar system; in the hopes of observing how the interstellar boundary changes with time. Scientists were expecting the distribution to be relatively even at any given time; with some differences along the Sun’s axis of rotation, and at the nose and tail of the solar system. Not only were these differences largely not present, but there was also a “ribbon” of higher emissions circling the sky. Scientists have since pinned down the ribbon as most likely being due to the galactic magnetic field, although why the other effects are weaker than expected is not as well understood. (Heerikhuisen “Pick-Up Ions”, L127)

The goal of this particular project was not to determine the cause of the ribbon, but instead to determine if there were any trends in how the ribbon has changed over the first three years of the IBEX mission (the 2013 maps are not complete and my not ever be completed due to technical issues with the now aging satellite). Maps from this project indicate that the ribbon weakened over the three year period in question.

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This image from the IBEX science team (McComas et al, 961) shows the ribbon mapped onto a sphere representing the outer edge of the solar system. The red arrow indicates the direction we are moving through the galaxy, while the black lines indicate the galactic magnetic field.