NASA spacecraft have found particles streaming into the solar system from interstellar space likely changed direction during the last 40 years, scientists say.

The finding allows mapping of Earth's location within the Milky Way galaxy, they said, and is crucial for understanding the planet's place in the cosmos over time -- where it came from, where it's currently located, and where it's going in its journey through the galaxy.

The results, based on data gathered by 11 different spacecraft during four decades, yield valuable clues to the size, structure and nature of the sun's heliosphere, the gigantic bubble that surrounds the solar system and helps shield Earth from dangerous incoming galactic radiation, the researchers said.

Interstellar gas clouds surrounding the solar system pass the sun at 50,000 mph, researchers said.

"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," study co-author Eberhard Moebius of the University of New Hampshire said. "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."

The direction of the wind obtained most recently by one spacecraft -- NASA's IBEX mission -- differs from the direction obtained from earlier measurements, which strongly suggests the wind itself has changed over time.

"Prior to this study, we were struggling to understand why our current measurements from IBEX differed from those of the past," Nathan Schwadron, lead scientist for the IBEX Science Operations Center at UNH, said. "We are finally able to resolve why these fundamental measurements have been changing with time: we are moving through a changing interstellar medium."