Interplanetary medium

The temperature in the outer region of the solar atmosphere (the corona) is very high. That is why certain particles in the corona have high enough velocity so that they can escape the gravitational attraction of the Sun. These escaping particles form the solar wind, a continuous plasma flow that the the Sun emits.

The magnetic field of the Sun fills the interplanetary space forming the heliosphere. In this area, only the magnetospheres of some planets (and ionized regions around active comets) are strong enough to keep the solar wind out.

The heliosphere is the area in which the total pressure of the solar wind plasma is stronger than that of the interstellar medium around it. It is therefore the result of an interaction between the solar wind and the interstellar medium into which the solar wind eventually merges.