The heliosphere is the magnetosphere, astrosphere and outermost atmospheric layer of the Sun. It takes shape in form of a vast, bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the Milky Way. As part of the interplanetary magnetic field, the heliosphere shields the Solar System from a significant amount of cosmic rays, including hazardous ionizing radiation (e.g. gamma rays). Its name was likely coined by Alexander J. Dessler, who is credited with first use of the word in scientific literature in 1967.[1] The scientific study of the heliosphere is heliophysics, which includes space weather and space climate.
Flowing unimpeded through the Solar System for billions of kilometres, the solar wind extends far beyond even the region of Pluto, until it encounters the "termination shock", where its motion slows abruptly due to the outside pressure of the interstellar medium. The "heliosheath", is a broad transitional region between the termination shock and the heliosphere's outmost edge, the "heliopause". The overall shape of the heliosphere resembles that of a comet; being roughly spherical on one side, with a long trailing tail opposite, known as "heliotail".
Two Voyager program spacecraft explored the outer reaches of the heliosphere, passing through the termination shock and the heliosheath. Voyager 1 encountered the heliopause on 25 August 2012, when the spacecraft measured a forty-fold sudden increase in plasma density.[2] Voyager 2traversed the heliopause on 5 November 2018.[3] Because the heliopause marks the boundarybetween matter originating from the Sun and matter originating from the rest of the galaxy, spacecraft that depart the heliosphere (such as the two Voyagers) are in interstellar space.
https://en.wikipedia.org/wiki/Heliosphere#Heliopause
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