Exploration Time Variations

The first all–sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow "ribbon" of enhanced ENA emissions. In recent studies, the IBEX team has compared the second set of sky maps to the first in order to assess the possibility of temporal changes over the 6 months between views of each portion of the sky. While the large–scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale. In particular, the IBEX team finds that (1) the overall ENA emissions coming from the outer heliosphere appear to be slightly lower in the second set of maps compared to the first, (2) both the north and south poles have significantly lower (~10–15%) ENA emissions in the second set of maps compared to the first across the energy range from 0.5 to 6 keV, and (3) the "knot" in the northern portion of the ribbon in the first maps is less bright and appears to have spread and/or dissipated by the time the second set was acquired. Finally, the spatial distribution of fluxes in the southernmost portion of the ribbon has evolved slightly, perhaps moving as much as 6° (one map pixel) equatorward on average. The observed large–scale stability and these systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy and help inform possible mechanisms for producing the IBEX ribbon. In the IBEX maps, the poles are monitored almost continuously, which provides an unprecedented opportunity to continuously monitor the time–varying heliosphere. Further, the existence of observations at varying energies provides information across time–scales from 1–3 years allowing insights of variability across multiple scales. These studies by IBEX allow significant transformational understanding of the evolution of the global heliosphere. These advances are critical for discovering how the interaction between the solar wind and local interstellar medium respond to our everchanging Sun and the changing conditions in the local galactic medium.

References:

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Reisenfeld, D.B., F. Allegrini, M. Bzowski, G.B. Crew, R. DeMajistre, P. Frisch, H.O. Funsten, S.A. Fuselier, P.H. Janzen, M.A. Kubiak, H. Kucharek, D.J. McComas, E. Roelof, and N.A. Schwadron, Variations in the heliospheric polar ENA flux observed by the Interstellar Boundary Explorer, ApJ, 747:110, doi:10.1088/0004-637X/747/2/110, 2012.

Allegrini, F., M. Bzowski, M.A. Dayeh, R. DeMajistre, M.I. Desai, H.O. Funsten, S.A. Fuselier, P.H. Janzen, M.A. Kubiak, D.J. McComas, D.B. Reisenfeld, N. Schwadron, R. Vanderspek, Exploring the time dispersion of the IBEX–Hi ENA spectra at the ecliptic poles, ApJ Lett., 749:L41, doi:10.1088/2041-8205/749/2/L41, 2012.