New data show that the particles streaming into the solar system from interstellar space seem to have changed direction over the last 40 years.
Scientists were first alerted to a possible change through measurements taken by NASA's Interstellar Boundary Explorer (IBEX) mission. The readings, according to the study published in the journal Science, differed from those derived by the Ulysses spacecraft during the 1990s.
Seeing this, the IBEX team compared IBEX's measurements to data gathered by 11 spacecraft between 1972 and 2011, thereby ruling out the possibility that the newer instruments were simply providing more accurate results.
Among the many spacecraft, three methods were used to measure the incoming interstellar wind, including the direct measurement of neutral helium atoms coursing through the inner solar system.
A final analysis of these separate measurements strongly supports the wind itself has changed over time, according to the researchers, based on the fact that the direction of the wind noted most recently by IBEX differs from the direction obtained from the earlier measurements.
"It was very surprising to find that changes in the interstellar flow show up on such short time scales because interstellar clouds are astronomically large," said Eberhard Mobius, University of New Hampshire principal scientist for the IBEX mission and co-author on the paper. "However, this finding may teach us about the dynamics at the edges of these clouds -- while clouds in the sky may drift along slowly, the edges often are quite fuzzy and dynamic. What we see could be the expression of such behavior."
Knowing this, the scientists argue, is key to mapping the solar system's location and movement within the Milky Way. Furthermore, the study opens up deeper insight into stellar winds themselves, which play a dynamic role in the size and structure of the Sun's heliosphere, or the bubble that surrounds the solar system, shielding us from incoming galactic radiation.
"Prior to this study, we were struggling to understand why our current measurements from IBEX differed from those of the past," says co-author Nathan Schwadron, lead scientist for the IBEX Science Operations Center at UNH. "We are finally able to resolve why these fundamental measurements have been changing with time: we are moving through a changing interstellar medium."
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