The National Aeronautics and Space Administration announced last year's event Monday, saying it marked the beginning of a new type of astronomy.

"The two STEREO spacecraft were launched in 2006 into Earth's orbit around the sun to obtain stereo pictures of the sun's surface and measure magnetic fields and ion fluxes associated with solar explosions," NASA said. "From June to October 2007, sensors aboard both STEREO spacecraft detected energetic neutral atoms originating from the same spot in the sky, where the sun plunges through the interstellar medium."

Mapping the region by means of neutral, or uncharged, atoms instead of light "heralds a new kind of astronomy using neutral atoms," said University of California-Berkeley Professor Robert Lin, lead scientist for the suprathermal electron sensors aboard the STEREO spacecraft.

"This is the first mapping of energetic neutral particles from the edge of the heliosphere," Lin said. The heliosphere is a bubble in space produced by the solar wind. It stretches from the sun to beyond the orbit of Pluto.

The complex research is reported in the journal Nature.