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Voyager 2’s Path to Interstellar Space

I want to talk about the Voyagers this morning and their continuing interstellar mission, but first, a quick correction. Yesterday in writing about New Horizons’ flyby of MU69, I made an inexplicable gaffe, referring to the event as occurring on the 19th rather than the 1st of January (without my morning coffee, I had evidently fixated on the ‘19’ of 2019). Several readers quickly spotted this in the article’s penultimate paragraph and I fixed it, but unfortunately the email subscribers received the uncorrected version. So for the record, we can look forward to the New Horizons flyby of MU69 on January 1, 2019 at 0533 UTC. Sorry about the error.

Let’s turn now to the Voyagers, and the question of how long they will stay alive. I often see 2025 cited as a possible terminus, with each spacecraft capable of communication with Earth and the operation of at least one instrument until then. If we make it to 2025, then Voyager 1 would be 160 AU out, and Voyager 2 will have reached 135 AU or thereabouts. In his book The Interstellar Age, Jim Bell — who worked as an intern on the Voyager science support team at JPL starting in 1980, with Voyager at Saturn — notes that cycling off some of the remaining instruments after 2020 could push the date further, maybe to the late 2020s.

After that? With steadily decreasing power levels, some heaters and engineering subsystems will have to be shut down, and with them the science instruments, starting with the most power-hungry. Low-power instruments like the magnetometer could likely stay on longer.

And then there’s this possibility. Stretching out their lifetimes might demand reducing the Voyagers’ output to an engineering signal and nothing else. Bell quotes Voyager project scientist Ed Stone: “As long as we have a few watts left, we’ll try to measure something.”

Working with nothing more than this faint signal, some science could be done simply by monitoring it over the years as it recedes. Keep Voyager doing science until 2027 and we will have achieved fifty years of science returns. Reduced to that single engineering signal, the Voyagers might stay in radio contact until the 2030s.

Image: This graphic shows the position of the Voyager 1 and Voyager 2 probes, relative to the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Voyager 1 crossed the heliopause, or the edge of the heliosphere, in 2012. Voyager 2 is still in the heliosheath, or the outermost part of the heliosphere. Credit: NASA/JPL-Caltech.

Bear in mind the conditions the Voyagers have to deal with even now. With more than 25 percent of their plutonium having decayed, power limitations are a real factor. If either Voyager passed by an interesting inner Oort object, the cameras could not be turned on because of the power drain, which would shut down their heaters. Continuing power demands from radio communications and the heaters create thorny problems for controllers.

Even so, we’re still doing good science. Today the focus is on a still active Voyager 2, which may be nearing interstellar space. Voyager 2 is now 17.7 billion kilometers from Earth, about 118 AU, and has been traveling through the outermost layers of the heliosphere since 2007. The solar wind dominates this malleable region, which changes during the Sun’s eleven year activity cycle. Solar flares and coronal mass ejections all factor into its size and shape. Ahead is the heliosphere’s outer boundary, the heliopause, beyond which lies interstellar space.

The Cosmic Ray Subsystem instrument on Voyager 2 is now picking up a 5 percent increase in the rate of cosmic rays hitting the spacecraft as compared with what we saw in early August. Moreover, the Low-Energy Charged Particle instrument is picking up an increase in higher-energy cosmic rays. The increases parallel what Voyager 1 found beginning in May, 2012, about three months before it exited the heliopause.

So we may be about to get another interstellar spacecraft. Says Ed Stone:

“We’re seeing a change in the environment around Voyager 2, there’s no doubt about that. We’re going to learn a lot in the coming months, but we still don’t know when we’ll reach the heliopause. We’re not there yet — that’s one thing I can say with confidence.”

We haven’t crossed the outer regions of the heliosphere with a functioning spacecraft more than once, so there is a lot to learn. Voyager 2 moves through a different part of the outer heliosphere — the heliosheath — than Voyager 1 did, so we can’t project too much into the timeline. We’ll simply have to keep monitoring the craft to see what happens.

What an extraordinary ride it has been, and here’s hoping we can keep both Voyagers alive as long as possible. Even when their power is definitively gone, they’ll still be inspiring our imaginations. We’re 300 years from the Inner Oort Cloud, and a whopping 30,000 years from the Oort Cloud’s outer edge. In 40,000 years, Voyager 2 will pass about 110,000 AU from the red dwarf Ross 248, which will at that time be the closest star to the Sun. Both spacecraft will eventually follow 250-million year orbits around the center of the Milky Way.

I return to Jim Bell, who waxes poetic at the thought. He envisions a far future when our remote descendants may be able to see the Voyagers again. Here is a breathtaking vision indeed:

Over time — enormous spans of time, as the gravity of passing stars and interacting galaxies jostles them as well as the stars in our galaxy — I imagine that the Voyagers will slowly rise out of the plane of our Milky Way, rising, rising ever higher above the surrounding disk of stars and gas and dust, as they once rose above the plane of their home stellar system. If our far-distant descendants remember them, then our patience, perseverance, and persistence could be rewarded with perspective when our species — whatever it has become — does, ultimately, follow them. The Voyagers will be long dormant when we catch them, but they will once again make our spirits soar as we gaze upon these most ancient of human artifacts, and then turn around and look back. I have no idea if they’ll still call it a selfie then, but regardless of what it’s called, the view of our home galaxy, from the outside, will be glorious to behold.


Comments on this entry are closed.

  • Thomas Goodey October 9, 2018, 14:23

    You say “Jim Bell… envisions a far future when our remote descendants may be able to see the Voyagers again.”

    I envision a much closer future when our quite close descendants will be able to see the Voyagers again. If things continue to proceed reasonably benignly, I have no doubt that, within a few hundred years, both of the Voyagers (and New Horizons as well) will be brought back to hang proudly in the Smithsonian.

    • ljk October 11, 2018, 12:38

      If the Voyager probes remain in deep space, they could last for several billion years at least. Bring them “home” to an Earth-bound museum, and you have shortened their existences to thousands of years at best.

      Besides, there are already several life-sized replicas at the Smithsonian Air and Space Museum and JPL. Do you think having the real ones will make a huge difference to most visitors?

      Let them remain in the galaxy. Sure, examine them down the road to see how space vessels handle the interstellar realm, but let them keep drifting through the void. An ETI society may thank us some day for letting them remain our galactic “ambassadors”.

  • Jesus Olmo October 9, 2018, 14:31


    A poem by Paul Mariani

    Beyond the moon, beyond planet blue
    and planet red, each day further
    from the sun she floats out toward

    the empty dark of X. Having done
    what she was sent out years before
    to do, she gave up sending even

    the faintest signals back to earth,
    to bend instead her shattered wings
    across her breast for warmth. It is

    late, he knows, and knows it will only
    go on getting later. He shifts alone
    in the late November light before

    her grave, as so often he has done
    these past five years, to try
    and finish what he knows to be

    unfinished business and must remain
    that way: this one-way dialogue
    between the self, and–in her absence–

    the mother in himself. Epilogue, perhaps,
    to what one man might do to heal
    the shaken ghost which must at last admit

    just how many years ago she logged off
    on her journey. So that now, as darkness
    drops about him like some discarded coat,

    old but useful, such as his mother used
    to wear, he takes it to him, much as
    she did, to ward against the cold.

    From ‘The Great Wheel’, published by W. W. Norton & Company, 1996. Copyright © 1996 by Paul Mariani.

    • H. Floyd October 10, 2018, 8:18

      Bob Geldof, holding up about as well now, wrote a magnificent anthem to Voyager 2 in its heyday with these days in mind:

      “Voyager 2 where are you now? Looking back at home and weeping, cold and alone in the dark void, winding down and bleeping. Ever dimmer, ever thinner, feebly cheeping in the solar winds — I’ll turn you up.

      Let me blaze a trail of glory across the sky, let me traipse across its golden high, let me marvel in wonder and unfettered gaze at the bigness and implausibility of being.

      Yes, stretch out your hands into infinity you human things, past blind moons and ice cream worlds, you hurl your metal ball of dull intelligence, and show us all your fragile grip…

      And I’m thinking big things,
      I’m thinking about mortality,
      I’m thinking it’s a cheap price that we pay for existence.”


  • steven Torry Rappolee October 9, 2018, 14:56

    plus some other objects to


    I would like to know what stars these objects might someday encounter

    • ljk October 10, 2018, 12:35

      Excellent information, thank you. While on a cosmic scale it may make little difference, these boosters are larger than the probes they sent into the wider galaxy. Plus they were once full of toxic and explosive fuel. More consideration should have been made as to their fates, but then again – especially concerning the Pioneers and Voyagers – we were fortunate enough that they were allowed by NASA et al to have information packages adorned to them.

      • ljk October 10, 2018, 12:37

        Just to be clear, the “they” I am referring to at the end of my paragraph were the deep space probes themselves. Yes, an edit function would be so very nice.

  • ljk October 9, 2018, 15:14

    Quoting from the article:

    “The Cosmic Ray Subsystem instrument on Voyager 2 is now picking up a 5 percent increase in the rate of cosmic rays hitting the spacecraft as compared with what we saw in early August. Moreover, the Low-Energy Charged Particle instrument is picking up an increase in higher-energy cosmic rays. The increases parallel what Voyager 1 found beginning in May, 2012, about three months before it exited the heliopause.”

    Is the heliopause shape uniform? It probably does not have to be a perfect sphere to have both Voyagers still exit that cosmic border around the same point, but I wonder if there is enough “wavering” due to solar and interstellar wind effects to perhaps have Voyager 2 leave either sooner or later than Voyager 1?

    As it has been conservatively estimated that the Voyager Interstellar Records’ exteriors will last at least one billion years in deep, deep space, the time periods listed in this piece will seem like a quick nap in comparison.

  • Jesus Olmo October 9, 2018, 16:42

    “The Farthest” – Full Lenght Documentary Film about Voyager Missions – “It is one of humankind’s greatest achievements. More than 12 billion miles away a tiny spaceship is leaving our Solar System and entering the void of deep space – the first human-made object ever to do so.”

  • Robin Datta October 9, 2018, 17:48

    Genetic drift can completely reshape species, has done so, and may continue to do so to our own. From the time the first lungfish scrambled ashore to our primate ancestors swinging in the forest canopy to the hominins (our lineage) that became us, change was mostly by the tiniest of increments, unrecognizable from one generation to the next.

    Future generations over similar expanses of time may acknowledge us in their phylogenic ancestry as we acknowledge some former lungfish, shrew, primate and hominin as our ancestors.

    Our artefacts may be about as interesting to them as the artifacts of bygone civilizations are to us. But some new and technologically young civilization may marvel at those artifacts.

    • john walker October 10, 2018, 7:00

      Genetic drift? It seems to me far more likely that intentional gene manipulation will lead to the evolution you elude to. Hardly recommended at the moment due to the huge gaps in our understanding, deliberate changes to the genome may potentially offer an increase in many of our base capabilities. This will be socially very disruptive at least initially. Id we overcome our inborn tribalist prejudices there may a future for a complete fracturing of our species into a multitude of offshoots. Hopefully without bias and exploitation. But for that our collective egos must be checked first.

      Also should our species settle on other worlds it seems only prudent to optimize our physis to the local conditions. Here the natural genetic drift you refer to may also occur at an accelerated rate independent of gene manipulation due primarily to gravitational influence.

    • john walker October 10, 2018, 7:05

      Spelling. I wish there was an edit function here.

    • ljk October 10, 2018, 12:28

      Robin Datta said on October 9, 2018, 17:48:

      “Our artefacts may be about as interesting to them as the artifacts of bygone civilizations are to us. But some new and technologically young civilization may marvel at those artifacts.”

      Are you saying that people would not find the history of their own species to be of interest? I can think of many archaeologists and historians who would strongly disagree with you. Not to mention the dangers of failing to learn from our history, which is quite in evidence at this moment in time.

      I invite you to read this article:


  • Mark October 9, 2018, 18:03

    I hate to burst your sentimental bubbles, but the future of these spacecrafts has already been written. One of the VoyaGERs returns to earth a few hundred years in the future, having been utterly augmented by alien technology, and poses an existential threat to our planet. The other gets blasted into smithereens as target practice for a Klingon ship. New Horizons is still an open book though.

    • ljk October 10, 2018, 12:06

      That was Voyager 6, which was supposedly launched in the late Twentieth Century (1999 to be more specific in some references). Since we only know of two spacefaring Voyagers, this must be one in an alternate universe, so we are safe – for now.

      Other evidence for the above is the fact that Voyager 6 only had a name plate adorned with just a couple of items from the Voyager Interstellar Record and Pioneer 10 and 11 plaques. Did they just get lazy? Did New Horizons with its deliberate avoidance of a formal information package influence them? And why did they make it so that even an advanced artificial ETI could not clean it off?

      We will not speak of the fate of Pioneer 10 in Star Trek 5, or of that film in general. Plus the plaque on that probe was facing outward, whereas in our Universe it was bolted on facing inward to reduce cosmic erosion. Though I wish someone had thought about placing the engraving on both sides of the plaque to increase its chances of being noticed and having its messages survive the eons.

      Plus, what was a Klingon warship doing so close to the Sol system? Pioneer 10 would not have gotten very far from our star system in just 300 years, so that means this Klingon vessel was way outside of its territory and much too deep in Federation space.

      • ljk October 11, 2018, 17:34

        Quoting from here:


        “Though depicted as being destroyed in Klingon territory in the late 23rd century, in actuality the spacecraft’s speed is so slow it will not reach Aldebaran for two million years. On its current trajectory, by 2287, Pioneer 10 should be roughly 820 AU from Earth (about 0.012 light years).”

  • john walker October 9, 2018, 18:09

    When I think of the distance through which Voyagers 22 watt transmitter must pass its data, it amazes me that the voice of this tiny drifting outpost of human civilisation can even still be heard. Those few square meters of earthan real estate have crossed a distance so very very far beyond anything we can physically even relate to. In the utter cold and in the center of an endless sphere of blackness seemingly frozen and unmoving despite its 17 odd km/s, it drifts now in desolate isolation beyond anything even Apollo experienced. Into this soul crushing void it floats ever further from the physical warmth and emotions of its Terran home and of its creators who still anticipate every one of those faint, faint signals. As the Suns rays shining on Voyager dim ever more, its own internal radiolytic light also dims. In the not so distant future it will broadcast its last whisper.
    I am glad that I don’t project any anthropomorphic character or sympathy onto this machine for if I did I would weep at its cold state and nearing demise.

    We peacefully seek knowledge. That is the light which illuminates our lives. And so even as physical darkness descends on Voyager, it carries the light of our searching minds into the cosmos. A sort of quiet satisfaction fills me at that thought.

    • Shaun October 10, 2018, 8:29


  • Paolo October 10, 2018, 0:50

    If some Entity would notice its passing by over there, It would gladly feel a profound est emotion by looking at the amount of desire, challenge and ingenuity embedded in it, inhabiting silently that awkward, cold contraption.

    • ljk October 10, 2018, 12:42

      Your observations remind me of this quote by Carl Sagan found in the 1978 Random House book he co-authored, Murmurs of Earth, about the Voyager Interstellar Record:

      “But one thing would be clear about us: No one sends a message on such a journey, to other worlds and beings, without a positive passion for the future. For all the possible vagaries of the message, they could be sure that we were a species endowed with hope and perseverance, at least a little intelligence, substantial generosity and a palpable zest to make contact with the cosmos.”


  • ljk October 10, 2018, 12:54

    Another take on the fates of Pioneer 10 and Voyager 1, this time by Orion’s Arm.

    Pioneer 10:


    Voyager 1:


  • ljk October 11, 2018, 11:29

    Voyager Status Update for 2018 to 2019:


  • Alex Tolley October 11, 2018, 17:47

    The previous post has 2015 TG387’s aphelion at 2300 AU, dwarfing the distance that the Voyagers have traveled and therefore must pass through the heliosphere spending most of their long orbit in interstellar space. The Voyagers have just reached twice the distance of its perihelion. The distances are staggering, making our solar systems known 8 (or should that be 9?) planets seem like our friendly, intimate backyards in comparison to the solar neighborhood.

  • ljk December 10, 2018, 10:46

    Voyager 2 is now just the second human-made space vessel to leave the Sol system:


    What about Pioneer 10 and 11? I know we lost contact with them in 2002 and 1995, respectively, but have they left the Sol system as defined by the Voyagers?