One rainy night in the mid-1980s I found myself in a small motel in the Cumberlands, having driven most of the day after a meeting and reaching Newport, TN before I decided to land for the night. It’s funny what you remember, but small details of that trip stick with me. I remember the nicking of the wiper blades as I approached Newport, the looming shapes of the mountains in the dark, and most of all the fact that I was thinking about an interstellar mission. I was working on a short story that grew out of the Voyager mission and the experience of those who controlled it.
After a late dinner at a restaurant near the motel, I asked myself what it would be like to be involved in a truly long-term mission. Suppose we develop the technologies to get a probe up to a few percent of the speed of light. If we send out a flyby mission to the nearest stars, we’re talking about a couple of centuries of flight time, or maybe a bit less. It’s inevitable, then, that a mission like this would be handed off from one generation to the next. Clearly the people who worked the stellar encounter would have been born and matured long after the mission left.
My story involved a man who worked on such a mission as the probe closed within a year of its encounter with Epsilon Indi, a man who learned that, although he was only in his 40s, he was dying and wouldn’t see the probe reach its destination. Back in those days the many avenues of exoplanet investigation weren’t yet clear and we had no good data on planets around other stars, so the big question was whether the probe would find planets around the star or not. But the larger issue was the human perspective on time and commitment even in the face of mortality.
I think about things like that every time I read the latest news from Voyager. The most recent information involves a so-called ‘magnetic highway’ and the behavior of charged particles in the heliosheath as Voyager 1 pushes closer to interstellar space. I can check this morning to see that the spacecraft is now 18,462,802,513 kilometers from the Earth, which works out to a one-way light time of just a bit over 17 hours. Voyager 1 was launched on the 5th of September, 1977, but it’s still a live presence that should keep sending back data perhaps for a decade.
There are surely people working around the periphery of the ongoing Voyager missions who weren’t born when they were launched. What would it be like for a civilization like ours to watch a true interstellar mission over the course of lifetimes, a deep space presence that, no matter what else we found ourselves doing would periodically galvanize the attention, reminding all of us that it was still out there, a heart still beating, a mind (human or artificial) still sending back data. There is something grand in that notion that calls up not just physics and astronomy but archaeology, the recovery of history and perspective, of humanity considered over deep time.
But of course when you’re working a mission, you have very practical work to do. Stamatios Krimigis (JHU/APL) is principal investigator of Voyager’s Low-Energy Charged Particle (LECP) instrument. Voyager 1 crossed the so-called ‘termination shock’ in late 2004 and moved into the heliosheath, where the solar wind has slowed and become turbulent. For a time the solar wind dropped to zero and the intensity of the magnetic field began to increase. I sense the practical scientist as well as a bit of the philosopher in Krimigis as he describes all this:
“The solar wind measurements speak to the unique abilities of the LECP detector, designed at APL nearly four decades ago. Where a device with no moving parts would have been safer – lessening the chance a part would break in space – our team took the risk to include a stepper motor that rotates the instrument 45 degrees every 192 seconds, allowing it to gather data in all directions and pick up something as dynamic as the solar wind. A device designed to work for 500,000 ‘steps’ and four years has been working for 35 years and well past 6 million steps.”
A four year design still functioning after 35 is a tribute to the engineering that conceived it and a reminder of the timescales that missions into much deeper space will one day have to reckon with. As to Voyager, has it entered a new region of space? This JHU/APL news release gives useful background: The LECP instrument has seen sudden increases in cosmic rays and decreases in low-energy particles, a varying scenario that has yet to settle down. Krimigis and team are saying that Voyager may be in a new region but not yet in true interstellar space.
Image: This artist’s concept shows plasma flows around NASA’s Voyager 1 spacecraft as it gets close to entering interstellar space. Voyager 1’s Low-Energy Charged Particle instrument detects the speed of the wind of plasma, or hot ionized gas, streaming off the sun. It detected the slowing of this wind – also known as the solar wind – to zero outward velocity in a region called the stagnation region. Scientists had expected that the solar wind would turn the corner as it felt the pressure of the interstellar magnetic field and the interstellar wind flow. But that did not happen, so scientists don’t know what to expect once Voyager actually crosses the heliopause. Credit: NASA/JPL-Caltech/The Johns Hopkins University Applied Physics Laboratory.
The term ‘magnetic highway’ comes up because in this region low-energy particles from inside the heliosphere are flowing out while higher-energy particles are flowing in — the Sun’s magnetic field lines are connected to interstellar magnetic field lines. While charged particles bounced in all directions before Voyager 1 entered this region, as if firmly contained by the surrounding heliosphere, they’re now much more directional. Krimigis again:
“If we were judging by the charged-particle data alone, I would have thought we were outside the heliosphere. In fact, our instrument has seen the low-energy particles taking the exit ramp toward interstellar space. But we need to look at what all the instruments are telling us and only time will tell whether our interpretations about this frontier are correct. One thing is certain – none of the theoretical models predicted any of Voyager’s observations over the past 10 years, so there is no guidance on what to expect.”
I suppose it was the ‘magnetic highway’ metaphor that brought back my night drive through the Cumberlands and all the musing about interstellar missions at a time when Voyager 2 had not yet reached Neptune (and Voyager 2, by the way, shows no signs of reaching the magnetic highway at a distance of about 15 billion kilometers from Earth). Voyager project scientist Ed Stone (Caltech), as venerable a figure as they come in the Voyager pantheon, thinks true interstellar space is a few months to a couple of years away for the farthest Voyager.
We’ll lose something priceless when the Voyagers finally go silent, but New Horizons is still robust and that gives me hope. I think we need a continuing voice from the deep dark to remind us that our nature is to explore even if human lifetimes fade to insignificance against the starry backdrop that bore us. Daily work is the thing, and to work for what Tennyson called ‘the long result’ is the best work there is, whether we’re there to see the end of the mission or not.