Where is the edge of the solar system? The accepted answer is that the solar system ends where the "solar wind" the material that flows from the top of the Sun's atmosphere - becomes so spread out that it is no longer able to push its way through the interstellar gas. However, before it gets this far the solar wind must pass through another important boundary known as the "termination shock". This is the region beyond which the solar wind, which is initially supersonic, suddenly becomes much slower. Its flow then becomes subsonic and eventually merges with the interstellar gas (see figure).
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