Most of us have a rather tidy image of the solar system. There’s the sun in the middle, a bunch of planets going around it, some large rocks strewn in between and around the perimeter, and then it’s the great void beyond. We’ve all grown up with the neat little graphs showing the orbits of the planets, as if that was all there was to see, and a neat line separated our little star family from everything else, like a nice little picket fence that tells us exactly when we’re on the inside versus the great beyond.
But where does the solar system truly end? How do we define the position of our imaginary line that marks the edge of our solar real estate?
Of course astronomers have solved this puzzle some time ago — in theory, at last. The edge of the solar system, it has been determined, is when the pressure of the solar wind from our sun is canceled out by similar pressure of leftover plasma from ancient supernova explosions that fills the vast area in between.
That line is unimaginably far away, and the intrepid Voyager 1 spacecraft made that crossover in August last year, but it’s only now that the discovery was actually confirmed. The science instrument that could have told us easily when that transition occurred failed quite some time ago, so scientists had to rely on other indirect measurements of solar plasma that they could evaluate with other detectors.
Lucky for them the sun produced a good amount of solar wind during the critical time and Voyager picked up those plasma traces when it reached its sensors thirteen months later, so the difference was quite pronounced, as the scientists were able to measure major ripples in the solar plasma.
Voyager passed through this area, going its usual one million miles a day, and now looking back at the data astronomers are able to make sense of the observations.
Voyager 1 is now the first man-made object to have jumped over the invisible picket fence, on the road to nowhere for a long, long time.
It has enough juice in its batteries left to communicate with Earth for another 10 years or so — and picking up the unimaginably faint signal is of course getting more and more challenging every day. During my visit to the giant Goldstone antennas this past summer I was able to witness a data download from the Voyager spacecraft. So it was just rows and rows of numbers, but to know that those numbers came from outside the solar system just boggles the mind — and the fact that we can still receive them and make sense of them.
It was quite a moving experience to see this incredible explorer call home faithfully at the appointed time, marked by a green line wandering across a moving display. Then the line ended, and another, different colored line began — another spacecraft calling home to leave a message.
Some 40,000 years from now Voyager will cross over into another solar system. Earth as we know it will no longer exist. As a species, we may vanish long before then. And perhaps some alien civilization will welcome this strange mechanical visitor — long dead but still faithfully carrying the greetings its creators charged it with — and perhaps they will learn from it, a message in a bottle from a long-gone family of explorers.
Check out Voyager’s message from Earth at http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html
Beate Czogalla is the Professor of Theater Design in the Department of Theatre and Dance at Georgia College & State University. She has had a lifelong interest in space exploration and has been a Solar System Ambassador for the Jet Propulsion Laboratory/ NASA for many years. She can be reached at email@example.com