On August 25th, 1986, a man-made object crossed the orbit of Jupiter, taking photos and real-time video of the planet and its moons as it passed. It used Jupiter’s massive gravitational pull as a slingshot, propelling it further into space, and two years later, it crossed the orbit of Saturn. As it passed Uranus and Neptune over the next several years, gaining speed as it hopped from planet to planet, it became the first man-made object to visit all four “gas giants,” or the massive planets in our outer solar system.
The voyage of this object has been a journey of firsts, a huge wealth of knowledge about the dynamics of our solar system, and is a starting point for our eventual exploration of the greater Universe. Fittingly, this project was named Voyager. And the Voyager probe is about to take another big step: it will soon leave our solar system for the desolate expanse of interstellar space.
NASA sent Voyager 2 was sent into space in August of 1977, and was followed two weeks later by its twin, Voyager 1. The goal of this mission was to take advantage of a rare planetary alignment of the gas giants in our solar system to obtain up-close information on our outer planets, which were poorly understood at the time. Most of what we know about Jupiter, Saturn, Uranus and Neptune come from images from telescopes, but these images from afar offer little information on the dynamic changes happening on each planet and the characteristics of their moons. Voyager 1 and 2 were timed perfectly to be able to capture information about these systems as they flew by, using their gravity to accelerate faster and faster until they would eventually depart from the solar system.
In space, there’s nothing to slow these probes down (not even friction, which requires air), so as they increase in speed from the gravity-assisted pushes of each planetary visit, they maintain it. Currently, Voyager 1 is about 13 billion miles from Earth, and made the transition into interstellar space in 2012. Voyager 2, which spent a little bit of extra time studying Uranus and Neptune, is about 11 billion miles from Earth, and will soon follow its brother into the emptiness of space.
Both are traveling at speeds close to 40,000 miles per hour and will continue to sail through the galaxy at this speed for the next several million years, maybe forever.
The journey of Voyager 2 through the outer planets brought a treasure trove of information to astronomers at NASA. Using measurement systems that, when developed in 1977, were monumentally ahead of their time, Voyager 2 took real-time photos and videos of all the gas planets and their moons as it flew by and transmitted them back to NASA.
Its equipment allowed it to determine the physical properties of both planets and their moons, describing their atmospheres, magnetic fields, gravity fields, densities, and masses, and even allowed us to determine the sizes of Saturn’s rings! As it flew past Jupiter, Voyager 2 photographed the planet’s ice-covered moon Europa and led to the discovery of an ocean underneath its icy surface, heated by the moon’s core. Voyager 2 transmitted photos of active volcanoes on another of Jupiter’s moons, Io, which were the first observed active volcanoes outside of planet earth, and remain the only ones witnessed to date.
The Voyager program illuminated oddities in our solar system that astronomers could never have predicted. As it flew by Saturn, Voyager 2 discovered an atmosphere on Titan, one of Saturn’s moons, whose nitrogen-rich composition makes it the object in our solar system with the closest atmosphere to that of our own.
At Uranus, the probe photographed 11 previously undiscovered moons, characterized a ring system surrounding Uranus (similar to Saturn’s) that we had not known existed, and through photos of the planet itself, discovered that Uranus’s south pole actually faces the sun due to its strange and extreme axial tilt. Astronomers now think that this inversion of Uranus’s axis is due to a collision with another planetary object sometime in the distant past, which knocked it off its axis and resulted in the planet now essentially spinning on its side.
At Neptune, Voyager 2 discovered 5 more moons, another ring system, and volcanoes that spew nitrogen ice on Neptune’s moon Triton, the coldest planetary body in the solar system. Voyager 2 is the only object to date to have visited Uranus and Neptune; most of what we know about these planets, we owe to this humble probe.
Small in size but massive in impact, Voyager 2 has changed fundamentally how we view the solar system, and our place inside it.
After cataloguing immense amounts of data on the outer planets, Voyager 2 sighed and prepared for its long, dark journey into the cosmos. Now, it continues at a speed of more than 35,000 miles per hour towards the true interstellar space outside the solar system, a void of nothing but interstellar plasma and high-intensity radiation from the galactic wind, and continues to transmit the data it collects to NASA.
Because space is so empty, there is next to no chance that Voyager 2 will ever collide with another object, and will therefore endure in the galaxy until it is destroyed by a neighboring supernova or collected by another intelligent species. For now, Voyager 2 will continue to help us understand the workings of the universe through measuring the clouds of material in the interstellar medium, the remainder of stars that exploded into supernovae over the past few billion years.
Voyager 2 still currently travels within the “heliosheath,” or the outer boundary of our solar system where the solar wind coming off our sun creates a sort of bubble of charged particles and magnetic fields around the solar system, protecting us from the radiation of interstellar space.
We will know for sure that the probe has left the heliosheath when it measures an increase in cosmic rays, the particles that originate outside the solar system and are blocked by our sun’s heliosphere. At a distance of more than 11 billion miles from earth, Voyager 2 will soon pass through this boundary and become an island, carrying the secrets of humanity, destined to wander the darkness of the Milky Way for an amount of time that we truly cannot comprehend.
Both Voyager probes carry a “golden record” with them, which contain an assortment of sounds and images found on Earth, in the event that the probe is intercepted someday by another intelligent civilization. The sounds of thunder, the songs of birds and whales, the whistle of wind and the crash of surf seem commonplace and fundamental to us, but they may be completely alien to other intelligent civilizations, especially those who may have left their home planets for the void of space. On this record the sounds of footsteps, laughter, and the cries of a baby represent humanity in all of our beautiful, delicate nuances.
The record contains images of human anatomy, of a slew of Earth’s creatures and landscapes, and of the solar system to give an idea of what our world looks like, while scientific formulas, the structure of DNA, and mathematical constants that hold true throughout the universe are portrayed to show our technological capacity and how we studied our world. Greetings in 55 human languages, songs from Bach and Beethoven, and even an hour long recording of the brainwaves of Ann Druyan, Voyager’s creative director, as she thought about the history of human civilization, of falling in love, and of the beauty of Earth’s landscapes made it onto this golden disc; that which may someday represent every human being on earth. With this memento of humanity the Voyager probes travel the cosmos, spreading our influence among the stars.
Voyager 2’s trajectory will take it towards Sirius, the brightest star in the sky, but even moving at speeds close to 40,000 miles per hour, it will not arrive in Sirius’ territory for another 296,000 years. Where will humans be in our evolution at that time? To put it into perspective, the first human beings that we are familiar with today evolved about 200,000 years ago. The agricultural revolution took place 10,000 years ago, and with it came the birth of civilization. The lightbulb was invented in 1879, the car came soon after that, and in 1963 we put men on the moon; in the 150 years or so since the industrial revolution, we have fundamentally changed ourselves and our world.
150 years was all it took to spark a technological revolution that is expanding to this day, endowing us with more power, more connectedness, and more potential.
So where, you ask, will we be in 296,000 years, when Voyager 2 reaches Sirius? It’s difficult to predict where we’ll be, or who we will become. But I doubt we will still be confined here on this fragile, bountiful little blue rock. By then, humanity may have ceased to exist, and a new species formed from our most distant descendants may have learned all there is to know about the Universe, and become like gods in their capacity. Maybe we will have been destroyed by our ambition long before then. Your guess is as good as mine.
When I think of space, I come alive. In my mind I see galaxies lit by starlight in myriad shapes and sizes, nebulae painted in technicolor across the black abyss, and beautiful black holes in deep space. New planets, maybe some filled with bizarre and abstract life, quasars and binary systems, comets trailed by ice and fire and supernovae that illuminate the expanse for light years. Space is more than human beings could ever hope to explore; in that, it humbles us. But there is little doubt that it is our final frontier. Like Voyager 2, we too are destined to someday toddle out of our nest to explore the mysteries hidden within an endless cosmos. Someday, maybe by the time Voyager 2 makes it to Sirius, or maybe long before, we will find our place among the stars.
For now a humble probe leads the charge, a sentry in the long night, eternalizing the legacy of humanity on the canvas of space-time as it navigates the universe in quiet observation.