In 2018 the space probe crossed the heliosphere, which is the bubble formed by the magnetic field of the Sun and solar winds that can reach speeds of three million kilometers per hour in which all the planets of the Solar System are housed.
The probe works like a wind sail in a strong breeze and according to Edward Stone, a professor at the California Institute of Technology and lead author of one of the five articles published in Nature Astronomy, it can be compared to a cosmic super-tanker that crosses the space.
Voyager 2 has compiled measurements that have allowed astronomers to confirm, first, that it has crossed into interstellar space, which makes it the second ship to do so, after its twin, Voyager 1, got it in 2012.
And, secondly, it has yielded information about the heliopause, the outermost structure of the heliosphere that acts as a boundary between it and the interstellar space, and of which until now nothing was known.
“When we launched the Voyager mission with the two ships in 1977 we had no idea about the bubble that the Sun creates around itself with the supersonic solar wind, the heliosphere. We didn’t know how big it was, nor if the ships would survive after reaching the end of the heliosphere and abandoning it to enter interstellar space,” said Stone.
The Voyager 1 and 2 ships were launched days apart and on different paths to explore Jupiter and Saturn. After fulfilling the objectives of their respective missions, both ships embarked on the path to interstellar space.
“That both ships, despite traveling on opposite paths, have crossed the heliopause at the same distance approximately from the Sun, implies that the heliosphere is symmetrical, at least at the two points where the Voyager ships crossed,” he said. Bill Kurth, from the University of Iowa, co-author of one of the studies.
Although Voyager 1 sent valuable data about that region to the end of the solar bubble to Earth, a failure in its plasma instrument in 1980 prevented it from taking complete data from that transition.
For that reason, the scientists could not directly identify the transition from the hot solar plasma to the coldest interstellar.
Voyager 2, on the other hand, has been able to record this step with direct and detailed measurements.
The plasma wave instrument of Voyager 2, which captured a jump in plasma density: while inside the solar bubble the plasma is hot and of lower density, in the interstellar space it is colder and high density.
Voyager observations near the heliopause show magnitudes of huge magnetic fields, large enough to form a spherical bubble around the Sun.
Also, unlike Voyager 1, the data from 2 suggest that the limit of the Heliosphere is thinner and softer, with a stronger interstellar magnetic field on the other side.
The researchers believe that Voyager 2 crossed the heliopause in less than a day and consider that the interstellar medium closest to that limit is hotter and more variable than they expected.
The Voyager 2 data have shown similarities, but also differences with respect to the crossing of the previous Voyager 1 and the researchers consider that they could be due to changes in solar activity levels and to different trajectories of the ships.