A NASA Small Explorer spacecraft launched in 2008 October to study the interactions between the solar wind and the interstellar medium. It does so by detecting so-called energetic neutral atoms (ENAs), created at the boundary of the heliosphere where the solar wind collides with interstellar gas. These atoms are accelerated into the inner Solar System where they are detected by IBEX in a highly elliptical orbit that takes it out to about 300 000 km from Earth, well outside the Earth’s magnetosphere.

http://www.nasa.gov/mission_pages/ibex/index.html Official mission website.