Mystery Behind Solar System's Giant Ribbon Solved?

A comparison between the observation of the IBEX “ribbon” (left) and a Heerikhuisen et al. simulation of what the ribbon should look like considering an interstellar magnetic field (right). Credit: NASA/IBEX/Heerikhuisen et al.

Last year, NASA’s Interstellar Boundary Explorer (IBEX) made a discovery so profound that scientists had a hard time describing what they were seeing. A vast ribbon located in the outermost reaches of the solar system had been spotted, a structure that had never been seen before. Now scientists believe the shape might be created by a huge reflection caused by particles bouncing off a galactic magnetic field.

IBEX isn’t an ordinary space telescope and this mystery ribbon isn’t emitting any light; the ribbon is in fact the source of very energetic neutral particles that are raining down on us after travelling over 100 AU (approximately 9 billion miles).

IBEX is designed to detect fast moving particles called energetic neutral atoms (or ENAs for short) created at the absolute boundary of our solar system known as the “heliopause.” This boundary separates the bubble-like heliosphere (which contains the sun, planets and solar wind) and interstellar space (i.e. the space between the stars).

Our sun is continuously pumping out energetic protons as the solar wind, and eventually these protons are carried to the heliopause. At this point, a process known as “charge exchange” can occur between these fast moving solar protons and slow moving neutral atoms (usually hydrogen) originating from interstellar space.

Should the two types of particles collide, the energetic solar particles can steal an electron from the interstellar neutral atoms, thereby producing ENAs. Some of these ENAs are then fired back toward Earth.

This interaction can be detected by IBEX as they travel in a straight line and not deflected by any magnetic fields. The satellite then traces the ENAs back to their origin, producing a map of the heliosphere. In the case of the “ribbon discovery,” IBEX was seeing intense ENA production from a mystery structure that appeared to be located beyond our solar system.

Now, this is where things start to get really interesting.

In December it was announced that the veteran Voyager probes currently flying toward the heliosphere measured an unexpected increase in magnetic field strength. Scientists believe that this increase is due to an unexpectedly large magnetic field threaded through a cloud of interstellar gas called the “Local Fluff.” Our solar system is currently speeding into this Fluff.

In research that was published in the Astrophysical Journal Letters, Jacob Heerikhuisen, a NASA Heliophysics Guest Investigator from the University of Alabama in Huntsville, believes the ribbon observed by IBEX is caused by an interstellar magnetic field, possibly relating to the Voyager probes’ discovery.

“We believe the ribbon is a reflection,” said Heerikhuisen. “It is where solar wind particles heading out into interstellar space are reflected back into the solar system by a galactic magnetic field.”

Therefore, the energetic protons traveling inside the solar wind encounter this “galactic magnetic field” and are manipulated in such a way that they are reflected back to where they came from (U-turn style).

It’s as if the solar protons “bounce” off an invisible magnetic wall. Then they undergo charge exchange to produce the ENAs. The ribbon-like structure IBEX is seeing is therefore a previously unknown (and rather eerie) magnetic field that exists beyond the heliosphere.

“This is an important finding,” said 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.”

This all sounds very exciting, but does IBEX have a practical purpose? Actually, yes, it could be used as a cosmic ray weather forecaster.

By monitoring the shape and distribution of this ENA ribbon, we can see how it changes with time. As the solar system passes through interstellar space (and the Local Fluff), this external magnetic field can squash and squeeze our heliosphere. When this happens, highly energetic (and damaging) cosmic rays can penetrate deeper into our solar system.

This could potentially have huge implications for life on Earth and future human spaceflight plans, as let’s face it, cosmic radiation is well known for causing damage to anything organic.

Source: NASA

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