had passed through the heliopause. Measurements from the spacecraft revealed a steady rise since May in collisions with high energy particles (above 70 MeV), which are thought to be cosmic rays emanating from supernova explosions far beyond the Solar System, with a sharp increase in these collisions in late August. At the same time, in late August, there was a dramatic drop in collisions with low-energy particles, which are thought to originate from the Sun. Ed Roelof, space scientist at Johns Hopkins University and principal investigator for the Low-Energy Charged Particle instrument on the spacecraft, declared that "most scientists involved with Voyager 1 would agree that [these two criteria] have been sufficiently satisfied". However, the last criterion for officially declaring that Voyager 1 had crossed the boundary, the expected change in magnetic field direction (from that of the Sun to that of the interstellar field beyond), had not been observed (the field had changed direction by only 2 degrees), which suggested to some that the nature of the edge of the heliosphere had been misjudged. On December 3, 2012, Voyager project scientist Ed Stone of the California Institute of Technology said, "Voyager has discovered a new region of the heliosphere that we had not realized was there. We're still inside, apparently. But the magnetic field now is connected to the outside. So it's like a highway letting particles in and out." The magnetic field in this region was 10 times more intense than Voyager 1 encountered before the termination shock. It was expected to be the last barrier before the spacecraft exited the Solar System completely and entered interstellar space. Interstellar medium In March 2013, it was announced that Voyager 1 might have become the first spacecraft to enter interstellar space, having detected a marked change in the plasma environment on August 25, 2012. However, until September 12, 2013, it was still an open question as to whether the new region was interstellar space or an unknown region of the Solar System. At that time, the former alternative was officially confirmed. In 2013 Voyager 1 was exiting the Solar System at a speed of about per year, while Voyager 2 is going slower, leaving the Solar System at per year. Each year, Voyager 1 increases its lead over Voyager 2. Voyager 1 reached a distance of from the Sun on May 18, 2016. On September 5, 2017, that had increased