By Grant Jacobs 13/12/2018

They charted our lives. As children we read of their plans and their laboured construction. We watched them delivered, blasted into the heavens by the Titans. From time to time we heard of their long journey. They sent us photographs as they passed the outer planets. This week the last left flew past the light of the sun to voyage the great beyond.

Titan launching Voyager 2We grew up in the era of exploring the outer planets. The arc of the lives of those adventurous probes mirror our own.

They were the travellers of the Planetary Grand Tour. Not a day seized, but a rare, years-long alignment of the planets.

Some of us share their wanderlust to stray far to find the company of unfamiliar things. To visit those places and write to those home what it’s like out there.

Their older siblings were the Pioneers who left home in the early 1970s. The Pioneers passed Jupiter and Saturn, seeing new worlds nearby for the first time. They paved the way for their younger siblings to come.

Io transiting Jupiter
There’s something about a moon passing in front of planet to bring it home it’s really out there. (Sci-fi movie directors know this too.) Here Io transits Jupiter.

The Voyagers fled home later, in August and September of 1977. They first revisited the triumphs of their siblings. Like ambitious brothers or sisters they forged on further afield.

We coveted their photographs in National Geographic. It was the height of their fame.

Volcano on Io
The bright spot on the left is the volcano.

Their snapshots captured new things. Moons we’d never seen before. Great giant storms on faraway planets. Rocky, barren mini-worlds hurtling around them. A volcano erupting on Io.

The Pioneers fell to the long sleep and now drift in the deep. Their younger brethren are still with us, for now.

They’re travellers who visited far-away places who’ve kept going and left our neck of the galaxy.

They’re less active now. The fancy postcards no longer come. They multi-task less; their reports home now abbreviated notes of their surroundings.

For those that grew up with them, their slower pace glimpses into our own ever-closer future. Their diminishing lives urge us to see new places ere we too settle to drift.

Yet they still send messages home of where they’ve gone. We share their spirit out there.

Keep going, you good things. Go voyage the great beyond.


The occasion is Voyager 2 passing out into interstellar space recently, announced earlier this week.

The scale on the chart above it exponential. As you move away from the sun things are exponentially further away, as you can see from the numbers below the line. Those numbers are astronomical units. 1 AU is almost 150 million kilometres. 149,597,870,700 metres if you want to be picky. In around 40,000 years Voyager 2 will pass the star Ross 248. It’s travelling at better than 55,000 kph (relative to the sun).

Voyager 2 is now getting less ‘light’ from the sun than from rest of the galaxy. It’s travelling out beyond our solar wind, with the number of charged particles from the sun hitting the detector falling dramatically as the number of charged particles from the rest of the galaxy rise.

I guess what strikes a chord is that more than most space explorations this was a journey that continued on over time. Others had one specific target. Some set off to land on another world. A few orbited about them. But Voyager 2 in particular visited world after world and keep on going.

Although I’ve written in terms of Voyager 2, the Pioneers literally pioneered the way. Pioneer 11, for example, scoped the route through Saturn’s rings for Voyager 2. Voyager 1 passed out into interstellar space first.

The thing about Voyager 2, I guess, is it just simply keep knocking off more summits.

The Planetary Great Tour seized the opportunity of a chance that one craft could travel past all the outer planets. It was a rare opportunity. You can see something of how rare in this animated GIF –

Trajectory of Voyager 2

Voyager 2 is actually the first of the Voyagers sent into space. As Voyager 1 travels faster it overtook it. Voyager 1 continues to go further than Voyager 2.

Technology perspective

Younger readers should remember that digital photography didn’t come to consumers until years later after these probes left. Photographs of remote worlds had stunning impact. Today we take for granted that we can record images digitally and transmit them.

Another useful perspective might be what the computers of the day were like. The first widely-available general-purpose personal computers weren’t available until the time that the Pioneer and Voyager spacecraft were already out amongst the outer planets. (Remember they took years to get there.)[2]

The power source for the Voyagers slowly grows weaker. The RTG (Radioisotope thermoelectric generator) unit loses about 4 watts a year. Some instruments have been shut down and I understand they only run one instrument at a time now. Eventually they won’t be able to communicate to earth.

But they’ll continue to fly among the stars for a long, long time to come.


  1. Voyager 2 discovered 11 previously unknown moons of Uranus: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck and Perdita.
  2. The ‘1977 trinity’ were the Apple ][, the PET 2001 (aka the Commodore PET) and the TRS-80. Most people today will only recognise the name Apple. Modest-sized computers appeared before these, but they never took on the wider consumer market in the way that the 1977 machines did. In many ways personal computing didn’t really take off until the arrival of the 1980s computer + gaming machines and the IBM PC. The IBM PC didn’t arrive until the time Voyager 2 was out at Saturn. (PET stood for the very 1970s name, Personal Electronic Transactor. TRS stood for Tandy/Radio Shack, but a standing joke of the day was that it stood for ‘Totally Replaces Sex’.)

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About the featured image

All images from Wikimedia Commons. Originals are public domain via NASA, with the exception of the animated GIF which is the work of user Phoenix7777 (Creative Commons Attribution-Share Alike 4.0 International license).

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