Thursday, September 30, 2010

Knot In The Ribbon At The Edge Of The Solar System 'Unties'

The unusual "knot" in the bright, narrow ribbon of neutral atoms emanating in from the boundary between our solar system and interstellar space appears to have "untied," according to a paper published online in the Journal of Geophysical Research.

Researchers believe the ribbon, first revealed in maps produced by NASA's Interstellar Boundary Explorer (IBEX) spacecraft, forms in response to interactions between interstellar space and the heliosphere, the protective bubble in which the Earth and other planets reside. Sensitive neutral atom detectors aboard IBEX produce global maps of this region every six months.

One of the clear features visible in the IBEX maps is an apparent knot in the ribbon. Scientists were anxious to see how this structure would change with time. The second map showed that the knot in the ribbon somehow spread out. It is as if the knot in the ribbon was literally untangled over only six months. This visualization shows a close-up of the ribbon (green and red) superimposed on the stars and constellations in the nighttime sky. The animation begins by looking toward the nose of the heliosphere and then pans up and left to reveal the knot. The twisted structure superimposed on the map is an artist's conception of the tangled up ribbon. The animation then shows this structure untangling as we fade into the second map of the heliosphere. 
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Credit: IBEX Science Team/Goddard Scientific Visualization Studio/ESA

Analyses of the first map, released last fall, suggest the ribbon is somehow ordered by the direction of the local interstellar magnetic field outside the heliosphere, influencing the structure of the heliosphere more than researchers had previously believed. The knot feature seen in the northern portion of the ribbon in the first map stood apart from the rest of the ribbon as the brightest feature at higher energies.

While the second map, released publicly with the just-published paper, shows the large-scale structure of the ribbon to be generally stable within the six-month period, changes are also apparent. The polar regions of the ribbon display lower emissions and the knot diminishes by as much as a third and appears to "untie" as it spreads out to both lower and higher latitudes.

"What we're seeing is the knot pull apart as it spreads across a region of the ribbon," says Dr. David J. McComas, IBEX principal investigator and an assistant vice president at Southwest Research Institute in San Antonio. "To this day the science team can't agree on exactly what causes the knot or the ribbon, but by comparing different sky maps we find the surprising result that the region is changing over relatively short time periods. Now we have to figure out why."

The IBEX science team compares the first and second maps to reveal whether there are time variations in the ribbon or the more distributed emissions around the ribbon. This animation fades between the first and second IBEX maps. We see that the first and second maps are relatively similar; however, there are significant time variations as well. These time variations are forcing scientists to try to understand how the heliosphere can be changing so rapidly.
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Credit: IBEX Science Team/Goddard Space Flight Center

As the IBEX spacecraft gathers a wealth of new information about the dynamic interactions at the edge of the solar system — the region of space that shields our solar system from the majority of galactic cosmic ray radiation — the IBEX team continues to study numerous theories about the source of the ribbon and its unusual features.

The paper, "The evolving heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer," by D.J. McComas, M. Bzowski, P. Frisch, G.B. Crew, M.A. Dayeh, R. DeMajistre, H.O. Funsten, S.A. Fuselier, M. Gruntman, P. Janzen, M.A. Kubiak, G. Livadiotis, E. Mobius, D.B. Reisenfeld, and N.A. Schwadron, was published online Sept. 29 in the American Geophysical Union's Journal of Geophysical Research.

IBEX is the latest in NASA's series of low-cost, rapidly developed Small Explorers space missions. Southwest Research Institute in San Antonio leads and developed the mission with a team of national and international partners. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the Explorers Program for NASA's Science Mission Directorate in Washington.

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