It's been a rough year of going back and forth on exactly where Voyager 1 is these days, but NASA finally confirmed today that the spacecraft has officially become our very first interstellar traveler.
NASA already had a pretty good idea of what Voyager 1 would see when it entered interstellar space. When it finally started showing the right signs last summer, it didn't match all of what the scientists expected, though. It saw fewer particles from our Sun and more from particles from the galaxy, but due to a quirk of fate, the instrument needed to detect the sign that would clinch its passage into interstellar space — an increase in the density of the ionized gas (plasma) — wasn't working. A different instrument was giving them a 'proxy' reading, by watching for when the magnetic field around it would change from the direction the Sun's points to the direction the galaxy's points. Since they didn't see that change, they figured Voyager 1 still had a ways to go.
Now, though, NASA has finally been able to confirm that Voyager 1 entered interstellar space, either on or around the 25th of August, 2012.
It was a second quirk of fate that let them finally make this announcement. A massive eruption from the Sun's surface — a coronal mass ejection (CME) — blew off into space in March 2012, aimed directly at the area that Voyager 1 was in. The CME took 13 months to get out there, but when it finally arrived in April of this year, the spacecraft was able to detect the wave of vibrations it caused as it swept through the plasma there. These vibrations allowed scientists here on Earth to measure the density of the plasma, and they found that it matched what they expected to see in interstellar space.
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One interesting thing to note is that although Voyager 1 has left the heliosphere and entered interstellar space, it hasn't necessarily left our solar system. The Oort Cloud — the 'shell' of icy debris that surrounds our solar system, supposedly extends outwards for trillion of kilometres, so it's going to be some time before Voyager 1 actually passes through it (and Voyager's power supply is only going to last for another 7 years or so).
That's not to diminish this achievement, though, because this is great! It took over 36 years to do it, but something we humans built and launched finally made it to interstellar space!
(Image courtesy: NASA/JPL-Caltech)
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