One ‘light day’ for Voyager 1, a half a lifetime for this science journalist

Robotic space probe Voyager 1, the most distant object ever sent from Earth, will reach one light day away from Earth next year, a feat that has taken almost half a century to achieve.

Along with its twin, Voyager 2, these intrepid explorers are now more than 23 billion kilometres from Earth. By November of 2026, it will take 24 hours for a radio signal, travelling at the speed of light, to reach Voyager 1 and another 24 hours for a signal from the spacecraft to return to Earth. That means the scientists at mission control need to wait two days just to find out if the spacecraft is still alive. Voyager 2 is on a different, slightly slower flight path and will take another decade to reach that milestone.

Both spacecraft were launched from Cape Canaveral in 1977 on a reconnaissance mission to the giant outer planets Jupiter and Saturn. Voyager 2 continued on to Uranus and Neptune, making it the only spacecraft to visit those worlds. 

The gravitational influence of those giant worlds gave the Voyagers enough speed to escape the gravity of the sun. They are now leaving our solar system at more than 60,000 km/hr, which is fast by Earthly standards, but incredibly slow on the scale of our galaxy. 

I was fortunate to be at the launch of Voyager 2, along with Jon Lomberg, the space artist who designed the cover of the Golden Record, a message intended for any aliens who might find the spacecraft sometime in the very distant future. Jon and I met regularly over the years at the Jet Propulsion Laboratory in Pasadena California, which is mission control for many of NASA’s robotic spacecraft. That’s where scientists and journalists gather to examine images and data sent down from spacecraft that encounter the planets.

The Voyager mission was one of pure discovery, similar to explorers such as Magellan, who sailed forth to discover new worlds across the seas, except we were literally seeing new worlds beyond Earth.

The Voyager spacecrafts did not stop at any of the planets, instead they flew past at great speeds taking as many photographs and scientific measurements as possible along the way, like a traveller who never gets off a tour bus and takes as many pictures as possible out the windows.

The journey out to Neptune at the edge of our solar system took Voyager 2 twelve years, during which time Jon and I saw ourselves getting older, demonstrating how long it takes to cross our solar system.

The technology we were using to report on the mission also evolved from typewriters at the launch to portable computers that were more powerful than those on the spacecraft by the time we reached Neptune. 

Since then, while the Voyagers continue their journey between the stars, Jon and I have both gone grey, and some of the scientists, such as project scientist Ed Stone, have passed away. 

In other words, it takes the better part of a lifetime just to reach one light day in space. That puts the stars far beyond reach where distances are measured in light years.

If we take Voyager 1’s 50-year-journey to reach one light day, multiply that by 365, it will take 18,250 years to reach one light year, or 9.46 trillion kilometres, a standard unit of measurement in astronomy. Our closest star, Proxima Centauri, is 4.25 light years away, so Voyager would take 77,562 years just to reach our cosmic neighbour. Seventy seven thousand years ago, Neanderthals were still alive.

If you want to travel around our Milky Way Galaxy to visit the black hole at the centre, that is a journey of roughly 30,000 light years while the other side of the Milky Way is 100,000 light years distant. Do the math and that journey would take Voyager longer than the Earth has been in existence.

It’s been a profound experience to actually feel how slow we are by watching myself grow old as we take our first baby steps among the stars.– Bob McDonald

Space is big, really big, and we are like children who are still crawling out of the cradle of life, not able to walk or run. It will take Canadian astronaut Jeremy Hansen three days to reach the moon, and future astronauts will have to endure at least six months confined to a spaceship to get to Mars.

New propulsion systems such as plasma rockets promise to reduce travel times to the planets, but even these are still slow by interstellar standards. 

Back at the launch of Voyager, after the spacecraft roared off the launch pad and disappeared into the sky, we all became quiet and thoughtful about how long that object will be out there wandering among the stars.

Both spacecraft are expected to remain intact for a billion years, possibly more. During that time, the continents will move, the climate will change, humans may go extinct.

It is hard to fathom the distances in space and how long it takes to go anywhere, but it’s been a profound experience to actually feel how slow we are by watching myself grow old as we take our first baby steps among the stars.