Heliosphere

General
The heliosphere is the region of space dominated by the Sun. The edge of the heliosphere is a magnetic bubble-like medium and is located far beyond the orbit of Pluto. Plasma "blown" out from the Sun, known as the solar wind, creates and maintains this bubble against the outside pressure of the interstellar medium , the hydrogen and helium gas that permeates Milky Way Galaxy. The solar wind flows outward from the Sun until encountering the termination shock, where motion slows abruptly. The Voyager spacecraft have actively explored the outer reaches of the heliosphere, passing through the shock and entering the heliosheath, a transitional region which is in turn bounded by the outermost edge of the heliosphere, called the heliopause. The overall shape of the heliosphere is controlled by the interstellar medium, through which it is traveling, as well as the Sun, and does not appear to be perfectly spherical.

Union Law
In Union law the outer edge of the Heliosphere is also the boundary where a system can claim ownership of space. This legal definition was needed to define how far local laws can be used. For example certain local systems may prohibit gambling, a space ship within the Heliosphere of a system is bound by local laws, while it is not once outside the Heliosphere.[1]

The Heliosphere is also the boundary of local militia, no ship or vessel belonging to a local military force may operate or enforce authority beyond the Heliosphere (either Union Police or Rangers must then be consulted)

[1] Sytems with one government or a common system authority (like the Sol System for example)

[Note] On September 12, 2013, NASA announced that Voyager 1 had exited the heliosphere on August 25, 2012, when it measured a sudden increase in plasma density of about forty times. Because the heliopause marks one boundary between the Sun's solar wind and the rest of the galaxy, a spacecraft such as Voyager 1 which has departed the heliosphere can be said to have reached interstellar space.