Giant Ribbon Discovered at the Edge of the Solar System

October 15, 2009: For years, researchers have known that the solar system is surrounded by a vast bubble of magnetism. Called the “heliosphere,” it springs from the sun and extends far beyond the orbit of Pluto, providing a first line of defense against cosmic rays and interstellar clouds that try to enter our local space. Although the heliosphere is huge and literally fills the sky, it emits no light and no one has actually seen it.

Until now.

NASA’s IBEX (Interstellar Boundary Explorer) spacecraft has made the first all-sky maps of the heliosphere and the results have taken researchers by surprise. The maps are bisected by a bright, winding ribbon of unknown origin:

Above: IBEX’s all-sky map of energetic neutral atom emission reveals a bright filament of unknown origin. V1 and V2 indicate the positions of the Voyager spacecraft. [more]

But now, the mystery may be solved—

“This is a shocking new result,” says IBEX principal investigator Dave McComas of the Southwest Research Institute. “We had no idea this ribbon existed–or what has created it. Our previous ideas about the outer heliosphere are going to have to be revised.”

“We believe the ribbon is a reflection,” says Jacob Heerikhuisen, a NASA Heliophysics Guest Investigator from the University of Alabama in Huntsville. “It is where solar wind particles heading out into interstellar space are reflected back into the solar system by a galactic magnetic field.”
Heerikhuisen is the lead author of a paper reporting the results in the Jan. 10th edition of the Astrophysical Journal Letters.

“This is an important finding,” says Arik Posner, IBEX program scientist at NASA Headquarters. “Interstellar space just beyond the edge of the solar system is mostly unexplored territory. Now we know, there could be a strong, well-organized magnetic field sitting right on our doorstep.”

The IBEX data fit in nicely with recent results from Voyager. Voyager 1 and 2 are near the edge of the solar system and they also have sensed strong* magnetism nearby. Voyager measurements are relatively local to the spacecraft, however. IBEX is filling in the “big picture.” The ribbon it sees is vast and stretches almost all the way across the sky, suggesting that the magnetic field behind it must be equally vast.

Although maps of the ribbon (see below) seem to show a luminous body, the ribbon emits no light. Instead, it makes itself known via particles called “energetic neutral atoms” (ENAs)–mainly garden-variety hydrogen atoms. The ribbon emits these particles, which are picked up by IBEX in Earth orbit.

IBEX will monitor the ribbon closely in the months and years ahead,” says Posner. “We could see the shape of the ribbon change—and that would show us how we are interacting with the galaxy beyond.”

I still remember the days at Rice University when we were still trying to figure out exactly what the ‘northern lights were’ and where they came from.


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