NASA's twin STEREO spacecraft have been studying the sun since their launch in 2006. But the mission made a surprising and unexpected discovery by detecting particles from the edge of the solar system, and for the first time, scientists have now been able to map the region where the hot solar wind meets up with the cold interstellar medium. However, this wasn't done with optical instruments imaging in visible light, but by mapping the region by means of neutral, or uncharged, atoms. This...