As Voyager 1 nears its end, Emma Davidson reflects on what its journey, along with Pluto and its moon Charon, reveal about the beauty and power of symbiosis. In her essay, Emma shows how relationships and collaborations often within liminal spaces remain fundamental to addressing humanity’s deepening crises and Earth’s custodianship
We live in a moment where the wheels seem to be wobbling on so many of our systems: climate, economies, democracies, human relationships. The future feels precarious as we witness rainforests burn, capitalism destroying any hope of financial security for entire generations of young people, a global rise in authoritarian political leaders, genocide, an epidemic of loneliness and isolation.
Countless hours by philosophers, economists and scientists have been devoted to analysis of each of these systems – climate change and environmental destruction, the end of capitalism, the rise of fascism and civil unrest, and how we treat each other.
Perhaps the answers to our questions lie outside our own planet and the human systems we create here. The farther afield I look, the clearer some details of our own situation become. You can see further from the edge of a problem than you can from its centre.
* * *
Charon, the largest moon of the dwarf planet Pluto, is around half the size of the planet that it orbits.
For 48 years between the discovery of Pluto in 1930, and the discovery of Charon in 1978, their combined size was taken to be Pluto alone, not two separate astronomical bodies. The patch of rust-red at Charon’s north pole, produced by the release of methane and nitrogen, contains the very foundations for life to form. Known as Mordor, this patch of colour may have been created by gases escaping Pluto’s atmosphere and clinging onto Charon when the two bodies passed within a close enough distance in their shared orbit.
It is this shared orbit that is the most fascinating part of the story of the moon named after the ferryman who carried the dead across the river Styx, and the dwarf planet named after the ancient god of the underworld.
The barycentre of the orbits of the two bodies lies in neither Pluto nor Charon, but between the two of them. They have a symbiosis, a co-dependent relationship. Two separate objects in space, circling each other forever, with neither object holding absolute dominance over the gravitational pull. A once in 248-year event resulted in the discovery that the mass that appeared to be a bump on Pluto was actually a moon. This ultimately downgraded Pluto’s status, in 2006, from planet to dwarf planet. The argument centres on whether Pluto must be considered as a singular object, or in a collective sense with Charon. For the record, as someone who believes in the power of the collective, I still think of the Pluto-Charon symbiosis as a planet. Its identity lies in the liminal space between them, in the barycentre of their orbits. Their collective orbit of the sun takes so long that the entire history of the so-called nation of Australia fits within a single year on Pluto.
* * *
Some of the most important events in our lives occur in liminal spaces. In the gap between more significant, named spaces, we make discoveries and experience epiphanies.
In the quiet grey light between night and the fully risen sun of daytime, while on a morning walk, I check the growth of a correa shrub underneath the branches of a dead eucalypt. Next spring, I hope to see the correa’s flowers providing food for king parrots that have taken up residence in the tree hollow. The correa is not planted in a garden or park, but in the space between a footpath and someone’s back fence – an unremarked upon gap between named spaces in my neighbourhood, but one that can sustain life.
So, too, the liminal space between Charon and Pluto holds the key to how the two bodies function. The mystical workings of gravity shape and define each of them. Their arcs around each other, and around our shared Sun, set the physical conditions of temperature and light that determine how their geological properties might otherwise have sustained the evolution of life. And yet, that centre of gravity is as outside of Pluto as it is of Charon. Any change in the barycentre would forever alter both of them, but neither of them control it. It is a thing unto itself, a complicated dance for two bodies, performed at planetary scale.
We have images of Charon in which Mordor’s colour is visible, its smoother southern hemisphere discernible from the craters and spectacular cliffs of its northern hemisphere, thanks to the New Horizons spacecraft. Launched in 2006, the same year in which Pluto was downgraded in planetary status, New Horizons has travelled past Pluto and is headed for the Kuiper Belt at the edge of our solar system.
In addition to our understanding of physics and geology, New Horizons has provided us with images that spark creativity in thinking, and empathy for the beauty and miracle of our universe. Data that enables us to better understand that even at an interplanetary scale, within the Deep Time scale of change, symbiosis and collaboration are a necessary function of all lasting systems. Without Charon, Pluto’s orbit would be different, and as a consequence Pluto itself would be fundamentally other than what it is today.
In the same way, symbiosis and collective relationships are a fundamental building block for biodiversity here on our own planet. The small ant-blue butterfly, which lives and breeds in a reserve near my house in Canberra, has a symbiotic relationship with the coconut ant. In turn, the coconut ant requires a habitat with dead wood – especially eucalyptus and acacia trees – in which to build its nest. If we want the butterfly to survive, we must continue to allow trees in those reserves to grow, and then to die or drop branches as they naturally should. We must not give in to the urge to tidy up the landscape or to use it as firewood. If we fail, this tiny butterfly, listed as critically endangered in some States, will lose its last known breeding sites. We will be grieving the loss of yet another unique species whose ecosystem role is still not fully understood.
The tiny ant-blue butterfly and coconut ant and their equally minute lifecycle are at the other end of the scale from Charon and Pluto’s planetary mass and billions of years of existence. But each relies on a relationship with another whose base sits outside either of them. Perhaps humanity itself could learn from the world around us, both at close scale in the butterfly and at the edges of our solar system. Perhaps our ability to function requires us to work collectively with each other, despite abstract jurisdictional boundaries on maps or the semantics of value systems, to care for every one of us. Perhaps the barycentre of those human relationships sits outside of each of our own bodies, and in the Earth itself that we rely upon and must therefore also care for.
* * *
Every now and then, I check the Deep Space Network website for updates on who’s talking to our little robotic space adventurers. New Horizons is being tracked by the Deep Space Network’s Madrid site, and is now more than 9 billion kilometres away, in the Kuiper Belt. Here in Canberra, our own Deep Space Network satellite chats regularly with Voyager 1, an older spacecraft and the first human-made object to enter interstellar space – like an older sibling to New Horizons. A call and response to Voyager 1, more than 25 billion kilometres away, takes two days to complete.
When Voyager 1 launched in 1977, in the same year as the first Star Wars movie, its mission was intended to last only three years. But its nuclear power source enabled it to fly further than anyone could have predicted, and provide us with so much more information about our universe. It was never expected to live more than 47 years. And yet it has, with NASA carefully switching off its systems one by one to enable it to continue its travels and to send messages back home to us. In 1990, Voyager’s cameras were switched off, so we can no longer see what it sees. Its heating system has also been switched off, leaving its 1970s-engineered valves and copper wired circuits to the fates as it flies through space in absolute zero temperatures.
In 2012, Voyager experienced its own life-changing moment in liminal space. Our adventurous little friend crossed the heliopause – the boundary line where our Sun’s winds are no longer able to push outwards any further. Voyager tumbled over the edge and is now in interstellar space, between our own solar system and the next, somewhere out there in the Milky Way.
This means that Voyager 1 is never coming home. Once its power source ceases to function, it will no longer be able to send us any data about its location or what it is experiencing. Because it is outside the pull of our own Sun, it will continue to fall further into space, unable to return. It will approach the Camelopardalis constellation in around 40,000 years, but will not be able to show us the colours of its planets or stars. We will never know what effect the magnetic fields of other solar systems have on our little friend’s circuitry. It will not be possible to measure the impact of cosmic particles hitting its antennae, or how Voyager’s Earth-mined metals withstand absolute zero temperatures.
* * *
Voyager 1 is dying.
We know that the end is close now. In December 2023, it began returning binary code data that no longer made sense. We aren’t sure why – perhaps it was hit by a cosmic particle that caused a system memory problem. But we cannot see its memory, so we don’t know where the problem is. Like a loved one whose neurodegenerative condition prevents them from communicating with us, but who can still feel and hear and taste the world around them, Voyager was trying to tell us what was happening in words we could not decipher. In April 2024, NASA engineers were able to identify the chip that had been damaged. They rewrote code and stored it in other parts of the flight data subsystem memory to route around the damaged chip, and started to receive usable data from Voyager after a five-month gap. But sometime in the next decade, perhaps as early as 2030 or 2036, Voyager’s energy systems will run out, and no more data will ever be sent back to Earth.
Voyager will still be out there, still reaching things that we cannot see. But without the ability to communicate with us, our adventurous elder will cease to speak altogether, and will be gone to us. Without power, they will no longer be able to measure and detect the space around them.
Falling outwards forever, in the austere environment of interstellar space, Voyager’s silent and inactive metal body will outlast humanity itself. Our inability to talk to each other does not negate their journey continuing. We, and they, just won’t know what that journey is.
In my dreams, a quantum entanglement state between Voyager 1 and its twin on Earth means that we always know what state our friend is in, no matter how far apart they are. A bit like the two-body problem of the Pluto-Charon orbit, where a change in one will move the other. But it is just a dream, and Voyager has no quantum entangled twin.
Eventually, we lose contact with everything that has been close to us. But we remember what we have learned from that contact.
* * *
There is still much we do not know about the shared orbit of Pluto-Charon, or the symbiosis between the small ant-blue butterfly and coconut ants. Perhaps we will never know how they work, but we do know that they only work because their entities are connected. Acceptance of the unknowable is an uncomfortable lesson to learn from following the journeys of spacecraft towards the outer edges of our own solar system.
There are practical applications from space missions that we can put to more immediate use in improving our blue sky thinking about physics, quantum mechanics, and geology. Those learnings have given us great leaps forward in healthcare technology, information management, and data analysis.
The philosophical leaps forward matter too. It has allowed space in my mind to develop a richer and deeper understanding of my own purpose: to work collectively with others for the future of all species and the planet for which we are custodians.
We will likely never again see the investment of publicly owned resources into missions like New Horizons or the Voyager program, whose funding was cut by the United Stated government in their 2026 budget.
But while we can still track the journeys of these spacecraft, and while they are still able to send data back to us for analysis, we can feel gratitude for what we have learned about the universe, our place in it, and our purpose in caring for the miracle that any of this exists at all.
One of the greatest things I have learned from space research, billions of miles from where I write these words and where you read them, is about relationships. The relationship between humanity and the environment we live in. The most important relationships cannot be defined by any of us as individuals. Their barycentre lies forever in the liminal space between us. It is our responsibility to find ways to work in relationship to each other, and to the environmental systems we are part of, to ensure they continue to function in ways that enable all of this to continue.
* * *
Emma Davidson works in the university sector to improve diversity, equity and inclusion in technology. She was a Greens Minister in the ACT Government and National Convenor for the Women’s Electoral Lobby.
Feature image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. Charon and Pluto: Strikingly Different Worlds. Photo ID: PIA19966. Pluto (lower right) and Charon (upper left), taken by NASA’s New Horizons spacecraft as it passed through the Pluto system on 14 July 2015. Article image courtesy of Emma Davidson. Correa shrub in liminal space. Canberra, 2025.