Buzz Lightyear, the toy action figure, made the declaration “To infinity and beyond!” famous, but the Voyager 1 spacecraft made it real. Earlier this month, scientists confirmed that the probe, launched nearly four decades ago, has left our Solar System and has reached interstellar space.
The Voyager 1 is the first man-made object to make that extraordinary transition, a milestone on a par with other historical moments such as the first circumnavigation of the globe or putting a man on the moon. Mankind has finally ventured into the stars.
Two Voyager spacecraft were launched in September 1977 to study Jupiter, Saturn, Uranus and Neptune, the outer planets of our solar system. The spacecraft alerted us to active volcanoes on Io, one of Jupiter’s moons, gave us intimate glimpses of Saturn’s rings, and discovered many previously unknown moons around those planets. They finished that assignment in 1989, at which point they were directed to deep space, to continue a journey that will eventually take them to other stars and solar systems.
We are unlikely to know what they ever encounter: Voyager’s power sources will be exhausted in about a decade and while the space craft will continue on its journey, it will do so without instruments and transmitters.
Yet even without an electronic “tether” to Earth, the Voyager probes retain information about their origin. The probes are carrying gold phonographic records etched with music, greetings, sounds and images from Earth. It will be some time before they are needed: On its current path and its present speed — 45 km/second or 162,000 km/hour — the Voyager 1 will not approach another star for nearly 40,000 years.
The Voyager 1 is now about 19 billion km from Earth, so far away that radio signals sent from the spacecraft take 17 hours to arrive here. It entered interstellar space, the vast expanse between the stars, a year ago, on Aug. 25, 2012. Scientists have been debating when that transition occurred; they were able to confirm the leap this summer, when they did the calculations on sensor readings that showed a 100-fold increase in the number of photons that occupied each cubic meter of space.
Scientists had speculated that they would observe that increase when the Voyager 1 crossed the threshold of deep space, known as the heliopause. Voyager 2 has another five to seven years before it makes that transition: It is heading in a different direction.
Shortly after that, scientists will begin to turn off the instruments in the two probes, as their plutonium power sources exhaust themselves. In 2025, the two spacecraft will be completely out of power and will become silent.
But that will not be the end of their journeys. Traveling almost 1.6 million km a day, Voyager 1’s next rendezvous will be with a star in the constellation Camelopardalis named AC+79 3888, about 1.7 light years away, in some 40,000 years. That will only the first of many encounters: Absent a collision, Voyager 1 will be in orbit around the galaxy for billions of years.
Even in the inner reaches of truly outer space, the Voyager 1 continues to teach us about the universe. Its current transmissions are updating our understanding of interstellar magnetic fields.
Scientists believe that they are affected by the heliosphere, a sort of bubble of charged particles that is defined by our sun. Data from the Voyager 1 should provide unique insight into the physics of this hitherto unknown domain.
It is difficult to appreciate the scale of this achievement. Of course, the distance from the Earth is immense. The numbers are so great that we need another scale to make them comprehensible. The Voyager 1 is 121 Astronomical Units away, 121 times the distance between the Earth and the Sun.
No less great is the temporal distance between the Voyager 1 and today: It is nearly 40 years old, built before there were cellphones, portable computers or even compact discs. Yet this historical relic from the days when disco still ruled the planet, will be Earth’s calling card for tens of thousands, if not millions, of years. (For comparison, think about those old high school photos.)
Equally astounding is the very scale of this achievement in human history. Outer space is the benchmark for the unknown — as scientists probe the ocean floor, depths no less murky and unexplored, their efforts are equated with journeys into deep space. The very concept of interstellar travel — “travel between the stars” — has been relegated to the realm of the imagination.
Yet when humankind finally breaks through the barriers of our solar system and truly begins our voyage to the stars, the notice is buried on the science pages as a technological achievement rather than an extraordinary step in the evolution of our species.
We should celebrate this moment. We should revive our capacity for wonder by listening to the sounds the Voyager 1 has captured — yes, space is noisy. We should dream of the infinities beyond our solar system and try to channel that universe of opportunities.