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Caption: "The heliopause is the boundary at ∼ 120 AU from the Sun between the heliosphere (i.e., the solar magnetosphere and stellar-wind bubble (AKA astrophere)) and the interstellar medium (ISM) adjacent to the Solar System. As the solar wind approaches the heliopause, it slows suddenly, forming a shock wave called the termination shock of the solar wind." (Slightly edited.)

The termination shock is an inward-going shock wave from the heliopause. There is also an outward-going shock wave: a bow shock formed as the heliosphere plows through the adjacent ISM.

Features:

1. At the heliopause, the solar wind merges with the interstellar medium in a complicated way.

2. The Voyager Program probes (1977--2030s) launched in 1977 reached the vicinity of the heliopause at of order 120 AU from the Sun in the 2010s.

   To be exact, Voyager 1 (1977--2030s) crossed the heliopause 2012 Aug25 at 121 AU from the Sun (see Wikipedia: Heliosphere: Heliopause; Wikipedia: Voyager 1: Heliopause). Voyager 2 (1977--2030s) crossed the heliopause 2018 Nov05 at 119 AU from the Sun (see Wikipedia: Heliosphere: Heliopause; Wikipedia: Voyager 2: Interstellar mission).

3. More in situ information from the Voyager Program probes (1977--2030s) and other information will further elucidate the heliopause and surroundings.

   It's likely to be a rather complicated story, and so we will NOT go into it further.

4. Note that the heliopause is NOT the edge of the Solar System in yours truly's opinion since astronomical objects gravitationally bound to the Sun include the Oort cloud which extends outward to somewhere between 3,000 and 200,000 AU (0.03--3.2 ly, 0.01--1 Mpc) (see Wikipedia: Oort cloud).