The interstellar boundary is the interface between the Solar System and interstellar space. Our Solar System is surrounded by a protective magnetic bubble generated by solar wind ejected from the Sun – this bubble is called the heliosphere.
At the very edges of the Solar System, the heliosphere collides with material from elsewhere in the galaxy. At this boundary, dangerous electrically charged particles moving towards us from interstellar space are deflected by the magnetic field, but neutral particles (with no charge) slip past and continue in towards the Sun. The particles that pass through give us clues about the composition of interstellar space and how it differs from our own protected magnetic bubble in the Milky Way.
The Interstellar Boundary Explorer (IBEX) has been patrolling this border since 2009, intercepting the neutral atoms of galactic wind. It has shown that the chemical composition of our local bubble is very different from interstellar space. For example, our Solar System has significantly more oxygen than the interstellar medium. It is not yet known why, but this fundamental difference could provide clues as to how the Solar System and life were able to evolve.