What is the heliosphere?

The Sun constantly streams out the solar wind, which pushes against the thin gas between the stars and inflates a huge protective bubble called the heliosphere. The boundary where the solar wind is stopped by interstellar space is called the heliopause. Voyager 1 crossed the heliopause in August 2012 at about 121 astronomical units from the Sun, becoming the first human-made object in interstellar space. Voyager 2 followed in November 2018. The heliosphere helps shield the planets from much of the harmful cosmic radiation arriving from the galaxy.