Interstellar magnetic field decoded

Using data from Nasa's Interstellar Boundary Explorer (IBEX) to better describe space in our galactic neighborhood, a team of scientists has determined the strength and direction of the magnetic field outside the heliosphere.

Such information gives us a peek into the magnetic forces that dominate the galaxy beyond, teaching us more about our home in space.

The theory says that some solar wind protons are sent flying back towards the sun as neutral atoms after a complex series of charge exchanges, creating the IBEX ribbon, said lead author Eric Zirnstein from the Southwest Research Institute in San Antonio, adding that simulations and IBEX observations pinpoint this process, which takes anywhere from three to six years on average, as the most likely origin of the IBEX ribbon.

Outside the heliosphere lies the interstellar medium, with plasma that has different speed, density, and temperature than solar wind plasma, as well as neutral gases. These materials interact at the heliosphere's edge to create a region known as the inner heliosheath, bounded on the inside by the termination shock - which is more than twice as far from us as the orbit of Pluto - and on the outside by the heliopause, the boundary between the solar wind and the comparatively dense interstellar medium.

Some solar wind protons that flow out from the sun to this boundary region will gain an electron, making them neutral and allowing them to cross the heliopause. Once in the interstellar medium, they can lose that electron again, making them gyrate around the interstellar magnetic field. If those particles pick up another electron at the right place and time, they can be fired back into the heliosphere, travel all the way back toward Earth, and collide with IBEX's detector.

The particles carry information about all that interaction with the interstellar magnetic field and as they hit the detector they can give us unprecedented insight into the characteristics of that region of space.

Zirnstein noted that only Voyager 1 has ever made direct observations of the interstellar magnetic field, and those are close to the heliopause, where it's distorted. But this analysis provides a nice determination of its strength and direction farther out.

The new findings can be used to better understand how our space environment interacts with the interstellar environment beyond the heliopause, said researcher Eric Christian, IBEX program scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in this study. In turn, understanding that interaction could help explain the mystery of what causes the IBEX ribbon once and for all.

The study is published in Astrophysical Journal Letters.