Using simulations and data collected by NASA’s Interstellar Boundary Explorer (IBEX), a team of researchers has determined the strength and direction of the magnetic field located beyond the heliosphere, or the large magnetic bubble that surrounds our planet’s solar system.
As the US space agency explained in a statement, IBEX detected an oddity shortly after its 2008 launch. It found a thin sliver of space that contained more streaming particles than any other part of the sky. At the time, the origins of this unusual ribbon were unknown, but scientists saw it as a way to potentially observe phenomena located beyond our part of the galactic neighborhood.
Now, in a new study published this month in the Astrophysical Journal Letters, Eric Zirnstein, a space scientist at the Southwest Research Institute (SwRI) in San Antonio, Texas, and colleagues build upon one particular theory that claims that the particles in the IBEX ribbon are actually bits of solar material that are reflected back towards us after reaching the edge of the heliosphere.
The IBEX ribbon in question.
The heliosphere is filled with solar winds, which are the constant outflow of ionized gas (plasma) from the sun. Once these particles reach the edges of the magnetic bubble, the theory proposes that some of them are reflected back towards the sun as neutral atoms following a complex series of charge exchanges, Zirnstein explained. This results in the creation of the IBEX ribbon.
Breaking down how the process works
The simulations and observations analyzed by the Zirnstein’s team revealed that this particular process, which takes between three and six years to complete on average, is the “most likely” explanation for the IBEX ribbon. But what specifically causes this plasma to be reflected towards the sun?
Beyond the heliosphere, the scientists explained, is a region of space known as the interstellar medium. Here, there exists plasma that has a different velocity, temperature and density than the ionized gas that makes up the solar wind, as well as with neutral gases. These materials interact at the outer edge of the heliopshere to create a region known as the inner heliosheath.
On the inside of the inner heliosheath is the termination shock, or the point where the solar wind slows down to subsonic speeds due to interactions with the local interstellar medium. This causes compression, heating, and a change in the magnetic field. On the outside of the heliosheath is the heliopause, or the boundary separating the solar wind and denser interstellar medium.
Some solar wind protons that reach this boundary will gain an electron, making them neutral and allowing them to cross the heliopause. Once they reach the interstellar medium, that electron can once again be lost, causing them to gyrate around the interstellar magnetic field. In some cases, if the particles gain another electron under the right circumstances, they can again be fired into the heliosphere, travel back to Earth, and collide with the IBEX detector, according to NASA.
These particles contain information about their interactions with the interstellar magnetic field, and that analyzing that data “provides a nice determination” of the “strength and direction,” and other characteristics of that region of space, said Zirnstein.
Simulations match up with Voyager observations – in most cases
The characteristics of the interstellar magnetic field determine the direction of the various ribbon particles shot back to Earth, the researchers said. Simulations indicate that the most energetic of the particles originate from a different part of space than the least energetic ones, which provides new insight into how the interstellar magnetic field interacts with the heliosphere.
As part of their research, Zirnstein’s team used observations to create simulations of the IBEX ribbon’s origin. These simulations correctly predicted the locations of neutral ribbon particles of different energies, and created an interstellar magnetic field that, in most cases, agreed with both the measurements collected by Voyager 1 and other observed properties of the region.
Some of the simulations did not line up with data points were Voyager 1 and Voyager 2 crossed the termination shock, but the study authors believe that these discrepancies could be caused by a stronger-than-expected influence from the solar cycle, which would in turn alter the strength of the solar wind and change the distance to the termination shock in the probes’ directions.
“The new findings can be used to better understand how our space environment interacts with the interstellar environment beyond the heliopause,” said Eric Christian, a scientists working on the IBEX program scientist at the Goddard Space Flight Center in Maryland who was not part of the study. “In turn, understanding that interaction could help explain the mystery of what causes the IBEX ribbon once and for all.”
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Image credit: NASA/IBEX/Adler Planetarium
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