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Every day, we send a ping. A signal leaves Earth from one of three Deep Space Network sites 鈥� depending on the rotation of the planet, it originates in either California, Spain or Australia. A parabolic antenna projects radio waves towards the lonely outer reaches of the solar system, far beyond the planets. There, after 24 hours of travelling at the speed of light, they reach a small spacecraft hurtling away from us. Voyager 1 is the most distant human-made object from Earth, and on 18 November, it will reach 1 light day away: a milestone it was never meant to hit.

EARTH: Hello, Voyager 1. Are you still there?

VOYAGER 1: Yes, still here.

We have been doing this for almost half a century, with the time between messages sent and received expanding with every passing day. All of Voyager 1鈥檚 scientific instruments bar two have been shut off to conserve power 鈥� the magnetometer and plasma wave instrument are still humming along, though they may soon need to be switched off.

As our most distant emissary crosses into the unknown, we take stock of the profound insights it gained for every light second it has travelled so far, what it has shown us about our solar system 鈥� and what we have learned about ourselves in the process.

1977: Lift-off

When Voyager 1 and its twin, Voyager 2, launched in 1977, the duration of their mission was expected to be five years. Yet both remain operational and still take measurements. While Voyager 2 beat its partner to launch by a few days, it took a slower trajectory past Uranus and Neptune, and Voyager 1 quickly took the lead 鈥� it will be another nine years before Voyager 2 slips beyond a light day away.

1977: Navigating the asteroid belt

After it departed Earth, Voyager 1鈥檚 first big task was to journey through the asteroid belt that lies between the orbits of Mars and Jupiter. This nine-month period was spent in a cruise phase with the scientific instruments off, conserving power for the craft鈥檚 time near the giant planets. Unlike representations in science fiction, the asteroid belt is fairly sparse, with around 1 million kilometres, on average, separating any two asteroids, so there was little danger of Voyager 1 hitting anything. During this time, it overtook its sibling craft, Voyager 2, allowing it to reach Jupiter and Saturn first.

1979: Rings and volcanoes

Voyager 1鈥檚 visit to the Jupiter system was one of the most scientifically fruitful parts of its mission. It took more than 18,000 images of the gas giant and its moons, all much sharper than those from the Pioneer 10 and 11 spacecraft that had visited Jupiter in prior years. These led to groundbreaking discoveries, including Jupiter鈥檚 ring system, and the lightning strikes and auroral lights sparkling amid its swirling clouds. The flyby of Jupiter鈥檚 moons proved particularly illuminating, revealing them to be far more complex than anyone had previously imagined. 鈥淭he sense of novelty would probably not have been greater had we explored a different solar system,鈥� wrote imaging team lead Bradford Smith in a 1979 paper.

Enormous webs of ridges and fractures were found on the moons Ganymede and Europa, and Amalthea turned out to be elongated rather than spherical. Io鈥檚 volcanoes were spotted for the first time, an unexpected 鈥� and even shocking 鈥� finding. Smith called them 鈥減robably the most spectacular discovery of the Voyager mission鈥�. Data from Voyager 1 painted the entire Jupiter system as dynamic and diverse, and the flyby marked the beginning of an epic and ongoing undertaking to better understand it.

1980: A menagerie of moons

The Saturn system flyby was the end of Voyager 1鈥檚 primary mission. Over just two days, it shed unprecedented light on Saturn, its rings, its moons and the complex interplay between them. Regarding the planet itself, measurements from the wide-field imager revealed how different Saturn鈥檚 circulation is from Jupiter鈥檚, teaching us volumes about how the atmospheres of giant planets work. They unveiled intricate details of Saturn鈥檚 rings and the fact that particles fall from the rings towards the planet. 鈥淭he atmosphere of discovery was absolutely intense at the planetary flybys: many of us were reluctant to go to sleep for fear of missing something,鈥� says William Kurth at the University of Iowa. 鈥淭here was no doubt we were rewriting textbooks in real time and our colleagues would be poring over the data for years to come.鈥�

For the first time, the combination of the moon Enceladus鈥檚 strangely bright surface and the structure of Saturn鈥檚 faint, outermost ring led researchers to suggest it may come from particles spewing out from the icy moon. It was also suggested that Enceladus might have liquid water beneath its surface. Both suggestions turned out to be true. As for the other moons, eight of them that had previously been seen only as distant dots finally had their surfaces revealed. Voyager 1 also discovered three new inner moons. But the crown jewels of the Saturn observation campaign were the close-ups of Titan, the only moon in the solar system with a thick, relatively Earth-like atmosphere. These observations were the first to unveil its structure and atmosphere, hinting at how similar to Earth 鈥� and how potentially ripe for life 鈥� it really is.

1980-1990: Express route outwards

The Voyager 2 spacecraft visited Neptune and Uranus, providing key insights into the ice giants, but Voyager 1 skipped them in favour of a faster route out of the solar system.

1990: The pale blue dot

From far beyond Neptune, 6 billion kilometres from the sun, Voyager 1 turned its cameras to look back towards home one last time before they were shut off for good. It took a series of 60 images, capturing the sun, Venus, Earth, Jupiter, Saturn, Uranus and Neptune, for a mosaic that became known as the 鈥渇amily portrait鈥� of the solar system. Mercury was too close to the sun to be seen, and Mars was obscured by a stray sunbeam. This remains the only time our home solar system has ever been photographed as a whole. The mosaic was the brainchild of astronomer Carl Sagan, who was a member of the Voyager team: he saw it as a way to demonstrate Earth鈥檚 place in the cosmos, with every planet appearing as a speck of light floating in the vacuum of space.

Despite its lack of detail, this series of pictures has become a poignant symbol of the vastness of space and the seeming uniqueness of our little blue world. The iconic image of Earth in particular, dubbed the 鈥減ale blue dot鈥�, took hold in the popular imagination, in part because of Sagan鈥檚 writing about it in his 1994 book of the same name. 鈥淭here is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world,鈥� he wrote. 鈥淭o me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we鈥檝e ever known.鈥�

1998: Most distant spacecraft

At about 10.3 billion kilometres from the sun, Voyager 1 overtook the Pioneer 10 spacecraft and became the most distant human-made object from Earth 鈥� a title it has retained ever since. No spacecraft launched to date is travelling fast enough to catch up, so it will remain the most distant spacecraft for the foreseeable future.

2011: Measuring the Milky Way

Earth鈥檚 proximity to the sun has often made it tricky to take measurements of the wider Milky Way. In particular, solar interference made it impossible to measure our home galaxy鈥檚 Lyman-alpha radiation, a particular wavelength of light emitted during the hottest phase of a young star鈥檚 lifetime. Observed in other galaxies, it is a telltale sign of star formation. In our own, sunlight had long drowned it out.

But in 1993, out beyond the orbit of Neptune, Voyager 1 finally escaped the glare of the sun and measured Lyman-alpha radiation from the Milky Way for the first time 鈥� although researchers didn鈥檛 realise it until they reanalysed the data in 2011. We know much more about star formation in our own galaxy than in distant galaxies, so we can use this data to connect those two bodies of knowledge, making our measurements of the Milky Way a better laboratory in which to understand the rest of the universe.

2011: Traversing purgatory

The beginning of the end of our solar system is an area known as cosmic purgatory, or the stagnation region. About 18 billion kilometres from the sun, it is where the solar wind鈥檚 speed slows dramatically and stops bolstering the sun鈥檚 magnetic field against interstellar space. At the edge of its reach, the magnetic field is compressed as the solar wind suddenly hits resistance from the interstellar medium, doubling in strength and marking the edge of the solar system鈥檚 protective bubble, the heliosphere. While it had been theorised to exist, no spacecraft had ever travelled through cosmic purgatory before Voyager 1 in 2011.

鈥淣obody had imagined that the influence of the solar atmosphere would be that far away,鈥� says Stamatios Krimigis at Johns Hopkins University in Maryland. 鈥淲e were anticipating, if we continued much beyond Saturn, we would get new things, but not the kind of revolution that was produced by the Voyager spacecraft.鈥� While it crossed into the margins of the solar system, Voyager 1 measured a sharp increase in cosmic rays, hinting that particles from elsewhere in the galaxy are trickling into the solar system.

2012: Outward bound

The definition of the edge of the solar system is a slippery one 鈥� Voyager 1 may or may not be beyond it, depending on which line in the cosmic sand you prefer 鈥� but the very edge of the heliosphere is called the heliopause. The heliosphere has a long, comet-like tail, and in 2012 Voyager 1 exited on the opposite side of the sun from that tail, about 18.1 billion kilometres from the star. Most of its scientific instruments had long been switched off, but it continued to measure the plasma in its immediate environment. An extraordinary increase in the density of electrons surrounding it indicated it had entered interstellar space, the first human-made object to do so. The crossing gave us valuable data on the heliosphere鈥檚 properties, and our first direct data on interstellar space.

2026: One light day away

The Voyager 1 mission hasn鈥檛 just shown us the vastness of our solar system, though its unparalleled contributions to solar system science can鈥檛 be overlooked. It also revealed the vastness of our ambitions. Bolted to its side is a golden record (pictured), a sort of audiovisual time capsule depicting humanity and life on Earth. Should any intelligent life form find the spacecraft as it continues out into the universe, they will be able to tell where Earth is and who lives here. They will see Earth鈥檚 sights: its natural and architectural wonders, its snowflakes and seashells, its myriad peoples. They will hear its sounds: greetings in 55 languages, symphonies, songs, bird calls, the rumble of thunder, the rising of the tide. They will know how far Voyager 1 has travelled from home.

鈥淚 would hope finding Voyager would tell them that we are curious and seek knowledge about the universe,鈥� says Kurth, who has been on the Voyager team for more than 50 years. 鈥淚 hope they would realise that it takes many individuals working together as a team to send such a device into the unknown.鈥� And even if aliens never find our cosmic ambassador, we now know those things.

For those of us here on Earth, Voyager 1 represents a small tendril of humanity reaching out into the wider universe. 鈥淚 think it鈥檚 the distance that fascinates people, and it鈥檚 also the fact that now we have two observatories out beyond the influence of the sun鈥檚 atmosphere, out in the galaxy,鈥� says Krimigis. The idea that we have reached beyond not just Earth, but our entire solar system, is astounding 鈥� let alone the fact that against all odds, the spacecraft is still functioning and still producing science.

That is due in part to what Krimigis refers to as a 鈥渃onspiracy鈥� among the engineers on the original Voyager team to equip it with enough fuel to reach the outer solar system and perhaps beyond. 鈥淭he engineers made a pact to make no decision that would limit their ability to continue after the Saturn flybys,鈥� says Kurth. 鈥淐learly, this approach has worked.鈥� The degree to which the spacecraft still functions, though, astonishes even those who built it. For example, a part on the charged particle instrument was intended to last just past Saturn, designed to rotate 250 times. It has now spun more than 8.5 million times, even after the instrument heaters were turned off. It is out there at -61掳C, still chugging along. 鈥淚 was prepared to see the thing frozen in place, and I almost fainted when it was still working,鈥� says Krimigis.

While its functionality will eventually fade, Voyager 1 may well outlast humanity. The only way it would stop hurtling along its trajectory is if it were either captured by aliens or smashed into something, and it isn鈥檛 expected to pass near anything at all until it reaches the star Gliese 445, which is 17.1 light years 鈥� 6242 light days 鈥� away. Even then, it will stay well over a light year from the star. 鈥淲hen we realise that the next close passes will be 40,000 years from now, we realise that space is really empty: Voyager is going to keep going forever and ever and probably not run into anything,鈥� says Krimigis.

This brings our own tiny world, our pale blue dot, into cosmic perspective. 鈥淚 believe that this mission is very significant in two ways. One is that humanity was able to send a spacecraft outside our solar system proper and into the galaxy. But it also highlights how small an achievement that is when one looks at the grand picture,鈥� says Krimigis. 鈥淓verything is so far away, and we have a long way to go.鈥�

That is what Voyager 1 reminds us of. The reach of humanity is so long it is almost unimaginable, and yet we have only barely reached the edge of our solar system. The vast cosmos is still out there, unexplored. And even though we cannot press very far into it, Voyager 1 shows us that the further away we go, the better we can see our place in the universe.

EARTH: Hello, Voyager 1. Are you still there?

VOYAGER 1: Yes, still here. I have a long way to go.