NASA scientists have published papers that use data that Voyager 2 gathered a year ago when it made the crossing into interstellar space. On November 5, 2018, Voyager 2 became the second spacecraft in history to leave the heliosphere, which is the protective bubble produced by the sun.
As Voyager 2 made that historic crossing scientific data was being gathered about the conditions the spacecraft was in. Scientists published five new papers that focus on observations during that transition. Each of the papers details findings that were gathered from one of the five operating science instruments aboard the spacecraft.
The operating instruments include a magnetic field sensor, two instruments to detect energetic particles in different energy ranges, and two instruments for studying plasma. When the data is taken together, it helps scientists to gather an image of what the transition into interstellar space is like. Scientists note that the plasma inside the heliosphere is hot and sparse, while the plasma in interstellar space is colder and denser.
The space between stars also contains cosmic rays, which are particles accelerated by exploding stars. Voyager 1 had discovered that the heliosphere protects the solar system from 70% of that radiation. When Voyager 2 exited the heliosphere, the particle detectors notice dramatic changes. The scientists say that the rate of heliospheric particles detected by the instruments dropped dramatically. The rate of cosmic rays increased dramatically and remained high.
The new papers have determined that Voyager 2 is not yet in undisturbed interstellar space. It appears, like Voyager 1, that Voyager 2 is in a perturbed transitional region just beyond the heliosphere. The team says that without the data from Voyager 2, they wouldn’t know if the readings that Voyager 1 took were indicative of the entire heliosphere or just the area and time where Voyager 1 crossed.