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NASA is ready to call it: Voyager 1 has finally entered into interstellar space, for real this time. And, surprise, the satellite left for the interstellar a year ago, according to an analysis of the fog of particles surrounding the craft. Since about August 25, 2012 (or the day Neil Armstrong died), those particles have been galactic, not solar, in origin, meaning that NASA is now pretty confident Voyager 1 is just over the border and approaching the rest of the Milky Way galaxy. 

Ed Stone, the Voyager project scientist at the California Institute of Technology said in a press release that researchers were certain of Voyager's departure: "we can now answer the question we've all been asking -- 'Are we there yet?' Yes, we are," he said. And yet, today's announcement recalls at least one other round recent of headlines announcing Voyager 1's entry into the interstellar, leading some to wonder if our emergence into the interstellar is now just a game of crying (space) wolf. But the research behind those stories, from last March, was met with skepticism from NASA. So why did the agency jump on board the interstellar train this time? 


Scientists have been analyzing data from the satellite for signs of interstellar travel since 2004, when it first picked up a characteristic increased pressure from interstellar space on the heliosphere, or the mass of particles unleashed by the sun that forms a bubble around the solar system, NASA explained. And in the summer of 2012, scientists perked up their interest in Voyager 1's location even more after a steep drop off in the solar particles reaching the probe, indicating that the satellite was probably, at the very least, on the edge of crossing over. Today's announcement, based on a study published Thursday in Science, seems to clarify that the craft did actually leave for the interstellar late that summer. The new study relies on a roundabout method used by scientists to measure the density of the plasma, or the fog of particles surrounding the craft, one of the tell-tale signs scientists wanted to see as evidence of interstellar space. Because Voyager 1 doesn't have a sensor on board to measure it directly, they followed a "massive burst of solar wind and magnetic fields" released by the sun on its journey to Voyager one. NASA explains: 

When this unexpected gift from the sun eventually arrived at Voyager 1's location 13 months later, in April 2013, the plasma around the spacecraft began to vibrate like a violin string. On April 9, Voyager 1's plasma wave instrument detected the movement. The pitch of the oscillations helped scientists determine the density of the plasma. The particular oscillations meant the spacecraft was bathed in plasma more than 40 times denser than what they had encountered in the outer layer of the heliosphere. Density of this sort is to be expected in interstellar space.

For months, scientists have argued about previous studies suggesting that NASA had left for interstellar space. And even though many researchers are excited about the new finding, and pretty confident about what it means, there are sill a couple flags of caution flying in the air. 

First, according to Stone, it's not quite accurate to say, yet, that Voyager 1 is out of the solar system. The probe still feels some influence from the sun, and has yet to reach the Oort cloud, a ring of comets still under the influence of the sun's gravitational pull, yet living in interstellar space, as Nature explains. 

Second, not everyone's convinced this time. According to Science News, some Voyager scientists at the University of Michigan in Ann Arbor would really prefer everybody to wait a few years for Voyager 2 to reach its sibling's location. The second Voyager, you see, has a working plasma sensor. 

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