The results: the plasma was 40 times denser than
what Voyager 1 reported when it was in the outer layer
of the heliopause of the solar system.
Moreover, the density matched all expectations of
the plasma density of interstellar space.
“We literally jumped out of our seats when we saw
these oscillations in our data – they showed us the
spacecraft was in an entirely new region, comparable
to what was expected in interstellar space, and totally
different than in the solar bubble,” stated Don Gurnett,
lead plasma wave science team member from the
University of Iowa.
“Clearly we had passed through the heliopause,
which is the long-hypothesized boundary between the
solar plasma and the interstellar plasma.”
With this new data in hand, scientists then went
back into the Voyager 1 data archives from 2012 and
were able to discern a similar set of oscillations from
the October–November 2012 timeframe. Working
backward, the science team determined that the
oscillations in the plasma density field first appeared in
late August 2012.
The abrupt, durable change in the density of the
energetic particles around Voyager 1 on 25 August
2012 was much more than the probe’s entrance into
the magnetic superhighway. It was the date that
Voyager crossed the boundary into a space where no
probe had gone before: interstellar space.
“Voyager has boldly gone where no probe has
gone before, marking one of the most significant
This graphic tracks the behavior of the sun’s magnetic field and a
population of charged particles as the Voyager 1 spacecraft traveled through space in 2012. The top graphic (magenta) shows the
intensity of the magnetic field in nanoteslas. These data come from
Voyager’s magnetometer. The bottom graphic (blue) shows the
prevalence of lower-energy charged particles that originate from
inside our heliosphere, which is the bubble of charged particles
around our sun. These data come from the cosmic ray instrument.
Each time Voyager 1 entered this new region called the ‘magnetic
freeway,’ the population of these inside particles dropped. After
Aug. 25, the magnetic field intensity has held steady at the same
elevated level and the population of inside particles hit an all-time
low and has not changed.
Image credit: NASA/JPL-Caltech/GSFC/University of Delaware
Ed Stone, Voyager project scientist, California Institute of Technology,
holds a model of NASA’s Voyager spacecraft during a news conference held Sept. 12 to discuss the Voyager 1 spacecraft officially
Image: NASA/Carla Cioffi
venturing into interstellar space.
technological achievements in the annals of the
history of science, and adding a new chapter in
human scientific dreams and endeavors,” said John
Grunsfeld, NASA’s associate administrator for science
in Washington.
For the record, Voyager 1 G&fW'6VBF