Voyager 1 and Voyager 2 are two of the most important spacecrafts in the history of space and solar system exploration, and currently the only two man-made objects to go beyond the limits of the solar system. Voyager 1 crossed the termination shock, the area of space where solar wind and interstellar radiation collide, towards the end of 2004, followed closely by Voyager 2 which exited the solar system in August last year.

In fact, according to the predictions made using the data received from Voyager 1, Voyager 2 should have crossed the termination shock much later. Voyager 1 reached the northern edge of the heliosphere at a distance of 12.48 billion kilometers away from the Sun, while Voyager 2 crossed the termination shock at only 11.2 billion kilometers from the Sun through the southern region, suggesting that the shape of the heliosphere is asymmetrical and squashed in the southern region.

“The solar wind is blowing outward trying to inflate this bubble, and the pressure from interstellar wind is coming in,” said Edward Stone, physicist and Voyager project scientist at Caltech, who recently published the detailed findings of the two spacecrafts.