The solar wind is created by the outward expansion of plasma (a collection of charged particles) from the Sun's corona (outermost atmosphere). This plasma is continually heated to the point that the Sun's gravity can't hold it down. It then travels along the Sun's magnetic field lines that extend radially outward. As the Sun rotates (once every 27 days), it winds up its magnetic field lines above its polar regions into a large rotating spiral, creating a constant stream of "wind." Such emissions, or streamers, are thought to come from large bright patches called "coronal holes" in the Sun's corona, The magnetic field lines of these coronal holes extend outwards, their ends dragged by the solar wind. They extend so far that they form an interplanetary magnetic field (IMF), which surrounds all the planets in our solar system.