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Effects on the Global Heliosphere



IBEX Neutral Imaging of the Heliosheath Reveals the Effects of the Interstellar Magnetic Field on the Global Heliosphere
The Interstellar Boundary Explorer (IBEX) measures Energetic Neutral Atoms (ENA) from the global heliosphere. The ENA maps reveal roughly two significant structures: the IBEX ribbon, which is a narrow feature that extends across much of the sky where the line–of–sight is roughly perpendicular to the interstellar magnetic field; and the globally distributed flux that has more gradual chances and fills the entire sky. Unlike the IBEX Ribbon that was not predicted by any model prior to availability of IBEX observations, the globally distributed flux was predicted several years prior to the IBEX launch and emanates from the heliosheath where the solar wind is slowed down and heated as it is deflected back to the tail of the heliosphere by the interstellar flow and magnetic field. The IBEX team has developed very sophisticated numerical methods allowing the Ribbon to be separated from the globally distributed flux. The resulting maps of the globally distributed flux reveal properties of the heliosheath such as its thickness (~50 AU near the nose of the heliosphere) and its global structure. Remarkably, one of the recent discoveries is that the tail of the heliosphere is deflected in the direction of the interstellar magnetic field. This effect corroborates previous estimates of the interstellar magnetic field strength (~3 µG) and, like the IBEX Ribbon itself, shows the significance of the interstellar magnetic field in structuring our global heliosphere. In addition to these findings, the IBEX ribbon and the globally distributed flux have energy spectra that are extremely unique. The Ribbon tends to have an excess in the energy spectrum near solar wind energies, which supports the concept that the Ribbon is produced from solar wind, although the underlying physical mechanism remains a controversial. The mapping of the heliosphere by IBEX enables significant advances in our understanding of the global boundaries that surround our solar system and their interactions with the local galactic medium. These advances are important both for understanding how the heliosphere is created and responds the changes both from the Sun and the local galactic medium. The global boundaries surrounding our heliosphere protect the Earth and the solar system from the dangerous cosmic radiation that exists at high intensities in the galactic medium. By understanding the global heliosphere, we learn how the levels of cosmic radiation change at Earth, how these changes may affect the viability of human exploration of space in the future as well as Earth’s radiation environment.
References:

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Dayeh, M.A., D.J. McComas, F. Allegrini, B. DeMajistre, M.I. Desai, H.O. Funsten, P. Janzen, G. Livadiotis, B.M. Randol, D.B. Reisenfeld, N.A. Schwadron, and R. Vanderspek, Effects of fast and slow solar wind on the energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) at the heliospheric poles, ApJ, 749:50, doi:10.1088/0004-637X/749/1/50, 2012.

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