A new set of all-sky maps from NASA’s Interstellar Boundary Explorer (IBEX) shows that conditions at the edge of our Solar System are more dynamic than first thought.

IBEX monitors the conditions at the boundary between the local interstellar medium and the heliosphere – the protective bubble that shields and protects our Solar System. It measures energetic neutral atoms (ENAs) which are created in the interstellar boundary where solar wind particles collide with the interstellar medium. The ENAs race in towards the Sun at speeds ranging from 160,000 to over 3.5 million kilometres per hour.

The first data map released in October 2009 showed an unpredicted bright ribbon of energetic neutral atoms emanating towards the Sun from the edge of the Solar System. Now, a second set of maps based on another six-months of data collection, shows dramatic changes to that ribbon, which appears to have 'untied', although the large scale structure of the ribbon has remained stable.

“What we’re seeing is the knot pull apart as it spreads across a region of the ribbon,” says David McComas, IBEX principal investigator and an assistant vice president at Southwest Research Institute in San Antonio. “To this day the science team can’t agree on exactly what causes the knot or the ribbon, but by comparing different sky maps we find the surprising result that the region is changing over relatively short time periods. Now we have to figure out why.”

The IBEX team think that the ribbon is somehow ordered by the direction of the local interstellar magnetic field outside the heliosphere, but that this is influencing the structure of the heliosphere more than previously believed. In the first data set, the 'knot' feature displayed the highest energies, whereas now it has faded by as much as a third, and has spread out – untied – to lower and higher latitudes.

“Our discovery of changes over six months in the IBEX ribbon and other neutral atoms propagating in from the edge of our Solar System show that the interaction of our Sun and the galaxy is amazingly dynamic,” says McComas. “These variations are taking place on remarkably short timescales.”