https://www.jpl.nasa.gov/voyager/mission/timeline/#event-a-once-in-a-lifetime-alignment
I saw a news item yesterday that provided some welcome relief from politics, violence, white nationalists marching under Nazi flags, and the latest threats of nuclear war. A reminder, sorely needed, of why we bother; proof, little appreciated, that we are more than we seem to be day-to-day, as seen from the middle of the fray.
It came in the form of a very famous recording, now being offered to the public decades after an initial and very limited production run of only two units. Now anybody can buy one, which must seem strange to those who were there when the first pair was minted. They weren’t meant to be heard by any of us down here, you see. They were intended for other ears, if ears there were; so, decades ago, what were then the only two pressings ever meant to exist were sent out into deep space as gifts. They came with an instruction sheet on how to play them, it being assumed that the recipients would have no idea, otherwise, what to make of them. Therein lay the beauty and the hope of the exercise.
It was in 1977, when I was 16 years old and beginning High School, that NASA launched two probes, Voyagers 1 and 2, to take advantage of a once-in-a-lifetime opportunity known then as the “grand tour”. It had been calculated about a dozen years earlier that in 1977, each of the outer planets of our solar system would be at a point in its orbit such that it would be possible to send out a spacecraft that could visit all of them, on a journey that would take years to complete. It was the sort of opportunity we tend to miss, even to scoff at, but this time the urgent hopes of the scientists were met by a willingness to spend public dollars to make an astronomer’s dream come true.
Why was this such a rare opportunity? Why can’t we send a spacecraft to buzz by any collection of planets we wish, at any time we please? The answer lies in the old school Newtonian laws of physics, and the unfortunate reality that this isn’t Star Trek, we don’t have warp drives, and live in a very big solar system with lots of relentlessly moving parts.
All deep space probes are launched on top of rockets, but it isn’t continuous rocket thrust that gets them to where they’re going. It’s inertia – the tendency of objects in motion to stay in motion. Here on Earth, forces like friction and gravity tend to cancel this out, dissipating the energy of motion, and bringing any moving thing to a cold stop – which is the other side of the inertial coin. Once stopped, the formerly moving object will remain stationary unless more energy is expended to get it moving again, owing to the tendency of objects at rest to remain that way.
In space, which isn’t quite a vacuum, but near enough for our purposes, friction is absent, and gravity, once an object escapes the Earth’s gravity well, is either absent or emanating from some other object out there, which makes it a potential source of more energy, and therefore momentum. Once it’s accelerated by rocket to a certain velocity, a space probe tends to remain in motion at that speed, coasting along on inertia, and can be aimed to rendezvous with a specific point in distant space.
With the Voyager probes the trick was to rendezvous not with one, but several different points in space, one after the other, in a sequence spanning over a decade. Most of the time, it’s simply impossible for an object moving on inertia to visit a number of planets, one after another, because the planets, inconveniently, aren’t sitting out there motionless in a straight line in the way they’re depicted, for illustrative convenience, in textbooks. Each of them travels in its own orbit, so it’s like a series of horses running around a series of concentric race tracks, the outer tracks much bigger than the inner ones. The horses end up all over the place, relative to each other, sometimes coming quite close, sometimes running on opposite sides of the Sun. If you aim a probe at any one of them, any other is quite likely going to be out of reach, off somewhere in its own orbit, travelling toward a spot where the probe won’t be able to go. Remember, with everything out there moving all the time, the probe would somehow have to change its route to wind up precisely at the point that the target planet will occupy some years in the future, after the huge distance between planetary orbits can be travelled. Out there, with nothing aboard for propulsion, there’s only one way to change course – exploit the gravity of some other object. The possible trajectories from such a maneuver are fairly limited.
That was the wonder of 1977. The positions of the planets that year were aligned just so, enabling a probe sent to Jupiter to use that planet’s gravity to “slingshot” itself off on a trajectory that would take it to a rendezvous with the future position of Saturn, and from there to Uranus, and then on to Neptune, all in one mission. It was a glorious opportunity. Nobody alive in 1977 would ever see another like it.
So the Voyager probes were sent off to take the grand tour, heading for the distant planets. It took them until the Spring, and then the Summer, of 1979 to reach Jupiter, the first stop on the tour. Whipping around Jupiter, Voyager 1 reached Saturn, the next stop, in the Winter of 1980, and Voyager 2 got there in the Summer of 1981. From there, Voyager 2 went on by itself, and it wasn’t until early in 1986 that it reached Uranus. The subsequent trip to Neptune took until the Summer of 1989. Voyager 1 was still travelling all the while, of course, but its trajectory away from Saturn took it on a path up and out of the solar system, on an infinite trip away from us, out toward the stars. Setting it on this path was the only way to engineer a fly-by of Titan, Saturn’s huge and fascinating moon.
Neptune was the last stop. From there, Voyager 2 had nowhere to go but out, travelling into deep space. Voyager 1 was already out there, with nothing more to see, but just before they turned the cameras off, in 1990, Carl Sagan, the famous astrophysicist, persuaded the operators at NASA to order the probe to turn and take a parting shot of the Earth, from a distance of about 4 billion miles. There was no scientific reason to do so. It was purely emotional. Sagan wanted a farewell shot, is all, just as you or I would were we out there, contemplating our last chance to ever see home. The result was perhaps the most poignant and sobering image ever captured during the space program, perhaps even more powerful, in its way, than the first shot of Earth-rise taken by the crew of Apollo 8 as it rounded the Moon. From the distance of Voyager’s vantage point, Earth was barely perceptible. Capturing its image strained the resolution of the cameras, our whole planet occupying just a single pixel. The photo has come to be known as “the Pale Blue Dot”, with the Earth appearing, in the words of Sagan, as “a mote of dust suspended in a Sunbeam”.
Here it is, un-enhanced:
If you can’t make it out, this enhanced version should help:
Yes – that’s really us. All of us. On his PBS series Cosmos, Sagan’s commentary on the image was almost an elegy, and has haunted me ever since. Listen:
Like all of the most stunning Voyager images, the Pale Blue Dot was featured in National Geographic, which to some of us functioned as a geek version of Sports Illustrated, cataloguing the triumphs of the home team as it proceeded from venue to venue. I was 16 when it started. I was 28 when the last fly-by gave us images like this:
There was Neptune, up close, its picture in the pages of a magazine. The last stop. The thought that after all those years it was all over, that there was no next planetary rendezvous to come, and no more incredible Voyager images to look forward to, was a bit deflating. It took a little getting used to.
After its rendezvous with Neptune, Voyager 2 kept going, just like its stable mate, as obedient as ever to Newton’s laws of motion. It wasn’t until 2012 that Voyager 1, the first to light out for interstellar space, managed to depart the outermost reaches of the Sun’s zone of influence, known as the “heliosphere”, being the sphere within which energy from the Sun, in the form of particles known poetically as the “Solar Wind”, can still be felt (the point at which the Solar Wind no longer registers is called the “heliopause”). That didn’t mark the end of the conversation; the Voyagers aren’t Solar-powered. They run on the energy of radioactive decay from a supply of Plutonium held safely away from delicate instruments at the end of a long boom. Both of them will still be sending signals, infinitesimally tiny little pulses of radio energy, until some time, it’s reckoned, in the mid 2020s. Each signal now has a strength of something on the order of one trillionth of a watt.
The two of them, heading in different directions, are far away now, at distances of about 11 billion miles (Voyager 2) and 13 billion miles (Voyager 1) respectively. If my arithmetic is right, Voyager 1 will be about 17 billion miles away from us when it stops transmitting. Voyager 2 will be a little closer.
Until then, a few of the personnel who were there at the beginning, old hands well past retirement age, will still monitor the probes, for as long as they can.
Having fallen silent, they’ll still travel on, mute and cold, into distant space. The fastest objects ever created by human beings, they still plod at a glacial pace by the standards of interstellar travel. Voyager 1, for example, is headed for a star a little over 17 light years away, just around the corner in cosmic terms, and it’ll be about 40,000 years from now when it gets there. By then our species, which has only been around for roughly five times that, may well be extinct. Yet on board the Voyagers, something of us, who we were, and what we and the pale blue dot we called home were all about, will remain.
It was largely on Carl Sagan’s initiative that each Voyager probe mounts a copy of the now generally available long-playing record, pressed in gold, that contains sounds as diverse as whale song, a baby crying, the crash of thunder, the music of a symphony orchestra – and Chuck Berry too – and languages, sounds, and music from all over the world, including the sound of laughter, in a recording of Ann Druyan, soon to become Sagan’s wife.
This might seem a rather fatalistic gesture. Maybe somebody exists out there, maybe not. Maybe if somebody is out there they will, against inconceivably long odds, actually encounter our dead probe, discern the attached record, figure out how to play it from the pictographic instructions on its protective cover, and draw some meaning from the sounds it contains. Maybe not. Actually, most probably not. Don’t bet the mortgage.
It almost makes me cry, thinking of our two robot emissaries, dutifully toting our recorded message along on their lonely journeys through the infinite black.
So what?, you might well ask, realistically and perhaps not unkindly. What possible difference can it make? Our sad little golden LPs amount, in all likelihood, to the cosmic equivalent of shouting down a well. Nobody’s going to hear us. Meanwhile, we’ll go extinct, and over the long haul, if you want to apply the most coldly incisive logic, not only will our own planet and the Sun it orbits disappear, in a blaze about 5 billion years from now that’s unlikely to be observed by any of the alien astronomers that aren’t out there – everything in the Universe, perhaps even the whole freaking Universe itself, will inevitably be destroyed at some point after that.
This is the sad conclusion reached within our cosmology. At some point, the whole Universe, which despite all appearances is a finite bubble of space-time, must either contract to extinguish itself in a “Big Crunch”, or – more likely, given our growing understanding of the expansion of the Universe and the mysterious “dark energy” that propels it – expand forever and ever, until the laws of thermodynamics bring about a perpetual deep freeze. It may even be that the physics of particle decay will eventually render all its constituent atoms down to a listless soup of little bits of nothing, bouncing about in a dark, pointless void.
In that case, who cares about our hopeful little message in a bottle? And who cares, for that matter, for the things we learned from the Voyager probes, or anything else we’ve ever done or seen? Gray, in his famous Elegy, opined that the paths of glory lead only to the grave, a depressing thought that still manages to seem almost optimistic compared to what we now know about the cosmic future. At least others of our kind can stare down upon a grave, and perhaps remember and appreciate the lives we led before we were laid there. You can almost reconcile yourself to being gone but not forgotten. Unfortunately, such requires there to be someone to remember. There won’t be. We now understand that ultimately, all of our paths lead finally to nothing, within a void that is nowhere. Even our cold dead bones, along with the dirt that covers them, and indeed absolutely everything else, everywhere, will be gone.
So Big Deal. Yay. Everybody clap for joy. The primates dispatched a box into space, carrying a how-dee-do towards nobody, and meanwhile gleaned some info about the insignificant balls that orbit their meaningless star, itself sitting on the outskirts of a pointless galaxy, one among billions that don’t matter worth a pinch of the dog’s business, in a Universe bent on its own annihilation.
Why bother?
A Nobel Prize-winning physicist named Weinberg supplied an answer in 1977, the same year the Voyagers began their mission. It’s one of the two best expressions I’ve ever heard of the hope and sense of purpose that persists in our souls, somehow, even in the teeth of the disheartening truths that flow from knowing just where we stand. The following is from the final paragraph of The First Three Minutes, Weinberg’s book on the cosmology of the creation and expansion of the Universe in the immediate aftermath of the Big Bang:
But if there is no solace in the fruits of our research, there is at least some consolation in the research itself. Men and women are not content to comfort themselves with tales of gods and giants, or to confine their thoughts to the daily affairs of life; they also build telescopes and satellites and accelerators, and sit at their desks for endless hours working out the meaning of the data they gather. The effort to understand the universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy.
The Voyager probes, little bundles of ingenuity and hope sailing ever outward toward the distant stars, bearing our greetings to anyone who might be out there, will be lending our lives, every day until long, long after we die, the saving grace of tragedy. They’re a testament to our capacity for wonder, and our determination to dream. Yes, the chance our message will ever be received is vanishingly small. It’s still a chance. And even if there’s no one to hear us, we’ll shout it out to the Universe itself.
With the Voyagers, we’ve managed to achieve, in the void of interstellar space, the scribbling of the same poignant message we’ve been leaving behind ever since cave people blew mouthfuls of ochre over their hands to leave outlines on the walls of the subterranean caverns at Lascaux: We were here. And while we were here, as the existence of our probes will attest into the indefinite future, we did our best to understand.
Oh, and that other set of words to live by? They’re heard in the final verse of this brilliant, philosophical song by Jackson Browne:
the needlefish 