Heliopause
The Heliopause is the point at which the solar wind joins the interstellar medium or the stellar wind from other stars. It would be the limit of the Heliosphere.
It is a theoretical limit approximately circular or in the shape of a teardrop, which indicates the limit of influence of the Sun. It is located at the point in which the loss of pressure of the solar wind, caused by the dispersion inherent to its radial diffusion, equals the external pressure of the interstellar medium. A good home visualization of this effect is obtained in a sink where the stream of water creates a zone of laminar diffusion around the point where it hits the bottom. The size of this zone varies according to the flow and pressure of the stagnant water.
It marks the boundary between the solar system and interstellar space, and its actual distance from the Sun is unknown, although it is assumed to be less in the direction of the Sun's motion in the galaxy, and is known to lie beyond from Pluto's orbit. Comets, however, cross this limit, as their orbits are highly eccentric, extending out to 50,000 AU or more.
Voyager 1 was the first spacecraft to explore the Heliopause, in December 2004. Voyager 2 entered the Heliopause on August 30, 2007, about 10 billion miles from Voyager 1, and more than 9,000 miles from Voyager 1. million kilometers from the sun.
NASA announced on September 12, 2013, that Voyager 1 officially left the heliopause and entered interstellar space on August 25, 2012.