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Solar 'tsunami wave' helps confirm that Voyager 1 is in interstellar space
Tuesday, July 8, 2014, 12:09 - Roughly one year after the first signs were received that NASA's Voyager 1 spacecraft has entered interstellar space, scientists have confirmation of this fact, thanks to the Sun.
In summer of 2012, NASA's veteran Voyager 1 spacecraft began to return indications to scientists back here on Earth that it had reached a new milestone in its journey away from home - instruments on board detected an increase in the number of cosmic ray particles from the galaxy and a reduction in the number of particles seen from our Sun. The only data missing was a third clue that would have cinched it, which is seeing the direction of the magnetic field around the spacecraft flip, but the instrument on the spacecraft that could have detected this clue wasn't working. However, last year, NASA scientists lucked out, when the Sun blasted out two eruptions in early 2012. It took over a year for the solar matter thrown out by this eruption to reach where Voyager 1 was, but when it arrived, it set off vibrations in the diffuse plasma gases that surround the spacecraft, which was picked up by Voyager's plasma wave instrument. This allowed the scientists to confirm that Voyager 1 had, indeed, exited the Sun's heliosphere and had entered interstellar space.
However, in the time since then, doubts have been raised about this conclusion, based mostly on the fact Voyager 1 still isn't seeing any indication of the expected change of the magnetic field direction from that of the solar magnetic field to that of the galactic magnetic field.
Now, though, there is even more support that Voyager is in interstellar space. This is thanks to yet another eruption from the Sun, which threw out a coronal mass ejection - a 'tsunami wave' in space.
"The tsunami wave rings the plasma like a bell," said Ed Stone, the Voyager mission's project scientist at the California Institute of Technology, according to a NASA-JPL statement. "While the plasma wave instrument lets us measure the frequency of this ringing, the cosmic ray instrument reveals what struck the bell - the shock wave from the sun."
"All is not quiet around Voyager," said Don Gurnett of the University of Iowa, the principal investigator of Voyager 1's plasma wave instrument. "We're excited to analyze these new data. So far, we can say that it confirms we are in interstellar space."
Even with this confirmation of Voyager 1 having entered interstellar space, this does not mean that the spacecraft has left our solar system. The Sun's heliosphere reaches out quite far beyond the orbit of Pluto, to about 121 astronomical units (18 billion kilometres), but our solar system is considered to extend all the way out into the hypothetical Oort Cloud, thousands of astronomical units from the Sun.