3. The invisible buffer zone with space - atmospheres, magnetospheres and the solar wind
The existence of the solar wind was suggested from observations of comet tails about half a century ago. When a comet is tossed into the inner solar system, the dirty ice on its surface is vaporized, forming two tails that always point away from the Sun. One is a curved dust tail, pushed away from the Sun by the pressure of sunlight. The other is a straight ion tail that is affected by the solar wind.
The radial, supersonic outflow creates a huge bubble of electrons, protons and magnetic fields, with the Sun at the center and the planets inside, called the heliosphere, from Helios the Greek word for the "Sun". Within the heliosphere, conditions are regulated by the Sun. Its domain extends out to about 150 AU, or about 150 times the mean distance between the Earth and Sun, marking the outer boundary or edge of the solar system. Out there, the solar wind has become so weakened by expansion that it can no longer repel interstellar forces.
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Copyright 2010, Professor Kenneth R. Lang, Tufts University