About twelve billion miles from our planet Earth, there is an imponderable boundary that sets the edge of the Sun’s domain and the start of interstellar space. NASA’s Voyager 2, the longest-running space mission, traversed that frontier more than 40 years after its launch sent a weak signal from the other side which the experts have now decoded.
Voyager 2 is the second ever to move beyond the heliosphere; the supersonic charged particles streaming outwards from the Sun.
After flying the scenic route across the solar system and giving what remain the only close-up images of Uranus and Neptune. It crossed the threshold into interstellar space more than six years behind despite setting off a month ahead of its twin, Voyager 1. The Voyager 2 has given the most detailed look yet at the edge of our solar system despite the agency’s scientists having no idea at the outset that it would survive to see such landmark.
Prof Ed Stone said: We didn’t know how large the bubble was and we certainly didn’t know that the spacecraft could live long enough to reach the edge of the bubble and enter interstellar space.
It has has a distinct cosmic weather front which means a distinct boundary where charged particles spreading outwards from the Sun ; interstellar wind blowing in from supernovae that exploded millions of years ago. The Voyager 1 verified there was a boundary marked by a sudden drop in temperature and an increase in the density of charged particles, known as plasma.
Voyager 2 gave the second set of measurements which offers new insights into the nature of the heliosphere’s limits because on Voyager 1 a crucial instrument designed to measure the properties of plasma directly had broken in 1980.
It is published in five separate papers in Nature Astronomy which reveal that Voyager 2 found a much sharper, thinner heliosphere boundary than Voyager 1. The second data also gives some more insight into the shape of the heliosphere. Bill Kurth said: It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed. And he continued: That says that these two points on the surface are almost at the same distance.
It also gives additional clues to the thickness of the heliosheath which is the outer region of the heliosphere and the point where the solar wind piles up against the oncoming wind in interstellar space.