Jan. 25 - Mysterious band of particles holds clues to Solar System's future

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http://www.cosmosmagazine.com/node/3251/full

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David

Mysterious band of particles holds clues to Solar System's future

Monday, 25 January 2010

by Tony Phillips

Science@NASA

IBEX spacecraft's all-sky map reveals a bright ribbon of particles.

Credit: NASARelated articles

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HUNTSVILLE, USA: The ribbon of particles at the edge of the Solar System "shocked" NASA researchers when it was discovered last year. Now they say it is a reflection off a strong galactic magnetic field, and holds the clues to the future of the Solar System.

In October last year, NASA's IBEX (Interstellar Boundary Explorer) spacecraft made the first all-sky maps of the heliosphere - the bubble of magnetism that springs from the Sun and surrounds our Solar System.

The result was a map bisected by a bright, winding ribbon of unknown origin. At the time, NASA researchers called it a "shocking result" and puzzled over its origin.

Unexplored territory

"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 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-organised magnetic field sitting right on our doorstep."

Ribbon reveals vast magnetic field

The IBEX data fit in nicely with recent results from the Voyager spacecrafts. Voyager 1 and 2 are near the edge of the solar system and they also have sensed strong magnetism nearby.

The ribbon that IBEX 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 seem to show a luminous body, the ribbon emits no light. Instead, it makes itself known via particles called 'energetic neutral atoms' - mainly garden-variety hydrogen atoms. The ribbon emits these particles, which are picked up by IBEX in Earth orbit.

The reflection process posited by Heerikhuisen and his team involves multiple "charge exchange" reactions between protons and hydrogen atoms.

Particles escape from the Sun, forming what is called the 'solar wind'. As these particles escape the Solar System, approximately 100 astronomical units (or 15 billion km) away, they are met by an interstellar magnetic field.

Magnetic forces intercept the escaping particles and sling them right back where they came from.

"If this mechanism is correct - and not everyone agrees - then the shape of the ribbon is telling us a lot about the orientation of the magnetic field in our corner of the Milky Way galaxy," notes Heerikhuisen.

The Solar System's future

The Solar System is passing through a region of the Milky Way filled with cosmic rays and interstellar clouds. The magnetic field of our own sun, inflated by the solar wind into the bubble-like heliosphere, substantially protects us from these things. The heliosphere's size and shape are key factors in determining its shielding power and, thus, how many cosmic rays reach Earth.

However, the bubble itself is vulnerable to external fields. A strong magnetic field just outside the solar system could press against the heliosphere and interact with it in unknown ways. Scientists are unsure if this would this strengthen our natural shielding or weaken it.

"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."

This is an edited version of a story first published on the Science@NASA web site.

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