The heliosphere, in which the sun and planets reside, is a large bubble inflated from the inside by the high-speed solar wind blowing out from the sun.
Pressure from the solar wind, along with pressure from the surrounding interstellar medium, determines the size and shape of the heliosphere. The heliosphere also is responsible for shielding out one-tenth of the galactic radiation coming in from the interstellar medium. IBEX will be the first spacecraft to observe the invisible interactions occurring at this boundary.
The supersonic flow of solar wind abruptly slows at the termination shock, the innermost boundary of the solar system. The edge of the solar system is the heliopause. The bow shock pushes ahead through the interstellar medium as the heliosphere plows through the galaxy.
Last Update: 24 Jun 2011 (AMB)