They call it the pale blue dot. It is simultaneously one of the least striking photos you are ever likely to see yet at the same time, probably the most significant.
The only thing of real importance in the image is one single pale blue pixel. Yet the light captured in that pixel is coming from Earth. It’s what our entire home planet looks like from a distance of 6.4 billion kilometres.
It inspired the famous planetary scientist Carl Sagan to wrote his 1994 book, Pale Blue Dot: A Vision of the Human Future in Space. In it, he wrote, “Look again at that dot. That’s here. That’s home. That’s us.”
It was a realisation that even the team who masterminded the picture were not fully prepared for until they saw the image. “We all realised that what this actually shows is that the Earth is no more than a tiny speck among the stars. It was a very chilling picture,” says Garry Hunt, a founding member of the Voyager Imaging Team.
He uses the word ‘chilling’ advisedly because he says it really brought home to him just how fragile the Earth is. “It really brought it home to us that you cannot go and live on Mars, you can’t go and live on Titan, you can’t go and live on Enceladus. There is nowhere else we can go,” he says.
Hunt became involved in the Voyager mission when he was working at NASA’s Jet Propulsion Laboratory in California as an atmospheric physicist. He saw the mission as an opportunity to study the atmospheres of other planets and relate them to Earth. It set him on a path he has been travelling ever since.
“For many decades, I have been talking to audiences in schools, universities, and businesses – you name it – I’ll talk to anybody about climate change. And the first picture I always show is this picture of the Earth as a blue dot.”
The pale blue dot image was taken on 14 February 1990. It was just one of sixty images taken that day that were designed to capture most of the planets of the Solar System (Mercury and Pluto could not be imaged) from the spacecraft’s unique vantage point. Voyager 2 had encountered Jupiter, Saturn, Uranus and Neptune and was now heading into deep space.
“The mission was essentially over by that time and we wanted to finish with something really special,” says Hunt, “The planets were all in perfect alignment and we thought if we could take the family portrait of all the planets it would be wonderful. The imaging team said, this is our last thing, then we will turn the camera off.”
And NASA agreed but the team had to wait for the results. Although the image was taken in February, it could not be downloaded immediately because NASA’s Magellan and Galileo spacecraft were using all the bandwidth of the NASA Deep Space Network.
Only in March could the images begin to be downloaded. In total there were 640,000 pixels of data to be downloaded. That might not be much by modern image standards but when the spacecraft is 4 billion miles away and the antenna only has a few hundred Watts of power, it takes a long time.
By May, all the images were received, processed and made public.
The twin Voyager spacecraft left an enormous scientific legacy. They discovered the volcanoes on Jupiter’s moon Io, the underground ocean on Jupiter’s moon Europa. They gave us our first close up look at Saturn’s rings and the complex way they behave. Looking to the future, Hunt thinks that one destination is crying out for a return visit.
“Oh I’d go for Titan without question,” he says. This is because Titan is thought to be similar to the Earth before life began.
The Voyager team analysed its thick atmosphere in 1980, then the European Space Agency’s Huygens lander touched down on its surface in 2005. But Hunt thinks there is much more to do because of what it may be able to tell us about the primordial Earth. “There is no question that we’ve got to have a jolly good look at Titan,” he says.
He recognises that his stint on Voyager happened at a golden time. Space exploration was in its infancy, and there was a tremendous pioneering spirit that pervades the endeavour at that stage.
Now, he says, NASA is different.“It’s much tougher now because money is tight. It was tough in my day, but it’s very much tougher now. The joy of JPL was the ability to experiment, to try, to learn, to make mistakes. That’s more difficult now.”
And it is more than just money that is invested in these missions: it can be people’s whole careers. “I gave my first interview to the BBC about Voyager 48 years ago, and here I am this morning doing another interview about Voyager. When you go and watch a spacecraft launch, just imagine if it failed on the pad or some other aspect went wrong. People’s careers are destroyed.”
Luckily, that did not happen for Voyager, and in the three decades since the pale blue dot image was first released, its significance has only grown.
“I have been battling climate change since my research days in the late 60s and early 70s. In the 90s I was involved in the debate with businesses over whether climate change was important. And I lost. And I was horrified that I lost.
“But now, people are suddenly realising what is actually happening. The whole planet has got to work together and the Voyager picture is almost the badge that we should be looking at.
“It is certainly the Valentine’s Day card that Voyager is giving to everyone and saying ‘This is where you are, take note.’ You are a very frail fragment amongst all the stars,” says Hunt.