(Music)
Voyager 1 has left the bubble around the sun and entered interstellar space, the space between stars.
It's amazing that Voyager has operated 36 years.
(sound of launch)
Launched in 1977,
travelled passed the gas giant planets
and now off into interstellar space.
A radio telescope took a radio image of Voyager 1 spacecraft slightly over 11-billion miles from the Earth.
It's a very small radio dot amongst the sea of darkness.
We have an instrument on Voyager, which can measure the density of the ions,
the plasma, which is out there.
In March of 2012, it turns out there was a massive eruption from the sun,
which eventually reached Voyager 1 in April of 2013. When that blast wave reached Voyager,
it caused the plasma around Voyager
to vibrate or oscillate in a certain particular tone.
Literally, they're the sounds of interstellar space.
(Interstellar space sound file)
And by measuring that sound wave, we could measure the density of the plasma
and we're amazed to find out that we were in interstellar space.
This is a historic milestone in the great journeys
of exploration that have been undertaken by humankind.
What is quite remarkable when you think about it, that far off now at ever increasing distances,
there's this little vehicle, two of them, which were built here
many years ago and launched 36 years ago.
Now, on a journey that will basically last for billions of years.
