(Scientific American)
Astronomers have released the first results from the late 2018 passage of NASA’s Voyager 2 probe into interstellar space, revealing some notable differences to the first crossing made by its sister spacecraft, Voyager 1, in 2012. The data shows that although Voyager 1’s departure was fairly “messy,” the exit of Voyager 2 was much cleaner as it left our sun’s influence on its journey into the galaxy.
Using data from Voyager 2’s Plasma Science Experiment, an instrument that was not working on Voyager 1 during its earlier entry into interstellar space, scientists confirmed that Voyager 2’s exit occurred on November 5, 2018. That was when Voyager 2 registered a sudden decrease in the “solar wind” particles emanating from our sun, along with a concordant increase in the numbers of incoming galactic cosmic rays and the strength of the interstellar magnetic field. Taken together, these data showed the spacecraft had passed beyond a boundary of our sun’s influence known as the heliopause—loosely defined as the point at which interstellar space begins. Both of the Voyager probes were launched weeks apart in 1977 on a grand tour of the outer planets, and to date are the only human-built machines to have reached interstellar space.
In a series of papers published in the journal Nature Astronomy, five separate teams of scientists analyzed the data from Voyager 2 to compare its crossing with that of Voyager 1. Although it took Voyager 1 about 28 days to cross the heliopause after leaving the sun’s bubble of influence, known as the heliosphere, it took Voyager 2 less than a day to do so. “On Voyager 1 we found that even before we left the heliosphere we had two episodes where we were connected to the ‘outside,’” says Voyager project scientist Ed Stone, lead author on one of the papers. “On Voyager 2 it was just the opposite. We were outside, but we continued to see particles leaking from the inside.” Read more