More than 30 years ago, we launched two space craft on a long-shot, once in a lifetime mission to explore the outer planets. Today, the Voyager space probes are still making their long, lonely journeys outside the boundaries of our solar system. Amazingly, they are still functioning and still sending us data about the things they encounter. Now we know what the edge of the solar system looks like, but where will the Voyagers end up?
Five papers published in a recent issue of Nature explain the crossing of the termination shock, the outer edge of the solar system where the solar wind (particles expelled by the sun) dies off. Voyager 1 and Voyager 2 exited at opposite ends of the solar system (north and south, relative to the orientation of Earth), and found that the interstellar magnetic field alters the shape of the heliosheath. Voyager 2 discovered that the termination shock is much more dynamic than astronomers guessed, with the solar wind ebbing and surging like rippling waves at the beach. Voyager 1 found some mysterious cosmic rays that scientists haven't figured out yet, and researchers also learned that energized ions from interstellar space help push back against the solar wind.
It's incredible that the Voyagers are still working, considering that astronomers in the 70s weren't even sure if they would accomplish their primary mission to explore Saturn and Jupiter. The amount of data they have generated is immense - much of what we know about the outer planets, even today, is based on Voyagers' exploration. Their distance from Earth is difficult to comprehend - it takes more than 14 hours for radio signals from the probes to get back to us. Although their radioisotope generators will run out of power in the next few years, and their orientation thrusters will use up the last of their fuel, they will continue their steady flight into space at more than 30,000 mph. There's really nothing out there to damage them or slow them down, so they will be traveling for a long, long time. It will take tens of thousands of years before they're anywhere near another star, and it might be millions of years before their journey finally ends. They'll be carrying those weird golden records that Carl Sagan designed just in case, but if anyone ever finds them, they'll probably serve as an epitaph to a human race long since vanished.
You can check out a longer article I recently wrote about the Voyagers over at HowStuffWorks. Image by: NASA/JPL.
The laboratory at the end of the solar system. [Nobel Intent]