On its 35th birthday, the Voyager 1 spacecraft is a little closer to home than we had hoped it would be at this point.
The Voyagers, 1 and 2, are right at this moment speeding away from us towards interstellar space. But a paper out in Nature today reports that, despite recently showing signs that suggest the spacecraft is about to leave (any minute now!), Voyager 1 could still be well inside the solar system.
By now, scientists expected Voyager 1 to have reached the heliopause – the boundary between the solar system and the rest of space. The solar wind emitted from the sun is what defines the reach of the solar system. Interstellar space has its own medium that pushes back against the solar wind. Where the two meet, at the edge of the solar system, scientists expect the solar wind to be deflected from its usual path. But Voyager 1 is not yet showing such a change.
Whether this means that Voyager 1 isn't at the boundary or that our models of that boundary need to be rethought it not yet clear. We are in truly uncharted territory here.
Voyager 1 launched 35 years ago today, a few weeks after its partner Voyager 2 lifted off. Both spacecraft are still going strong, almost literally pushing the boundaries of our knowledge about the solar system.
But my favourite thing about the Voyager mission is not the science it is doing, groundbreaking though that is.
On an early episode of Radiolab, Ann Druyan recalls (from about 5 minutes in) how along with Carl Sagan she chose the music that was put on to the Golden Record that Voyager is carrying to the stars. Druyan was creative director of the Voyager Insterstellar Message Project that made the record and describes it as "building a cultural Noah's Ark".
The Golden Record contains the sounds of Mozart, Bach and Beethoven, greetings in 59 human languages and one non-human language (the humpback whale). It holds mathematical defintions, the parameters of the solar system, images of all the solar system planets, photographs of the diversity of life on Earth. and much more. All of this is encrypted in binary code, in the hope that one day, millions of years from now, it will reach someone who can use the instructions on the front of the record to decipher it.
But the Golden Record is less about what's on it and more about what it encapsulates. It was a statement about the place of humans in the universe. "We were saying: we want to be citizens of the cosmos, we want you to know about us," Druyan told Radiolab.
During the compiling of the Golden Record, something else happened. Druyan and Sagan fell in love. She had just found the perfect piece of Chinese music to put on to the record, and had called Carl straight away to tell him about it. By the end of the phone call, they were engaged.
Two days later she went to Bellevue Hospital in New York and meditated while the sounds of her brain and body were recorded. Now they are on that Golden Record, traveling at 35,000 miles an hour on a one way trip out of the solar system. Maybe in a billion years some alien civilisation will find the Voyagers and translate the data back into brain waves, into thoughts.
Ann Druyan's story captures the romance of the Golden Record and the Voyager mission. In fact, that very telling of the story on Radiolab inspired documentary filmaker Penny Lane to make The Voyagers, a short film that is a love letter to her own "fellow traveller". The film takes the Voyager mission and spins it out into a beautiful story of love and chance. I've watched it at least five times already – I recommend you watch it too.
Even now as it stands poised on the edge of the solar system, about to break through to into the unknown, Voyager 1 is faithfully sending back data. It may not be out of the solar system yet, but when it leaves Voyager 1 will be the only human made object in interstellar space. As Lane says in her film, the Voyagers will probably be the only evidence that we ever existed.
When we eventually lose contact with Voyager, we'll be losing a spacecraft that has taught us so much about our solar system. But we'll be gaining a foothold in the universe at large. I've got my fingers crossed that Voyager 1 will make it out soon into the vastness of space and teach us something new when it does.