Voyager 2 left Earth's orbit in 1977 a month before its twin Voyager 1, but took seven years longer to reach the heliosphere's outer limit some 18 billion kilometres (more than 11 billion miles) away. Shaped something like a windsock in a stiff breeze, the heliosphere is formed by the Sun's magnetic field and solar winds that can reach speeds of three million kilometres per hour.
It can be compared to a cosmic supertanker ploughing through space, said Edward Stone, a professor at the California Institute of Technology and lead author of one of five articles published in Nature Astronomy.
"As it moves through the interstellar medium" - the vast expanses of space between stellar fiefdoms - "there's a wave in front, just as with the bow of a ship," Stone told journalists by phone.
Scientists hoped to answer a number of questions by comparing data sent back by the two probes, which pierced the Sun's protective bubble at different angles and locations.
"We didn't have any good quantitative data of how big this bubble is that the Sun creates around itself with supersonic solar wind and ionised plasma speeding away in all directions," Stone said. Voyager 2 confirmed, for example, the existence of a "magnetic barrier" at the outer edge of the heliosphere that had been predicted by theory and observed by Voyager 1.
"But contrary to all expectations and predictions, the magnetic field direction did not change when Voyager 2 crossed the heliopause," Leonard Burlaga, a scientist at the NASA Goddard Space Flight Center and lead researcher for one of the studies, told AFP.
The so-called heliopause is the relatively thin contact boundary where solar wind of charged particles and interstellar wind collide. Scientists were also surprised that it took 80 days for Voyager 2 to cross this magnetic barrier, while its sister probe did so in less than a day.