“Consider again that dot. That’s here. That’s home. That’s us […] a mote of dust suspended in a sunbeam.” The astrophysicist and popularizer Carl Sagan wrote these words inspired by a photograph of the Earth taken on February 14, 1990 from a distance of 6 billion kilometres. The image, dubbed Pale Blue Dot, was obtained by the Voyager 1 probe on its path to the confines of the Solar System.
The photo, which now marks 25 years, shows a background in which the Earth can hardly be distinguished, a clear speck that occupies only 0.12 pixels of the 640,000 that make up the image. Due to the effect of the reflections of the Sun in the camera, the point seems to float in a beam of light. Sagan had a special motivation with this photograph, as indeed it was he who suggested that Voyager 1 turn its camera around to take this long distance selfie of the Earth. The images were transmitted by radio to the Earth base over three months, at five and a half hours per pixel.
The first human being to lay their eyes on this historic document was the planetary scientist Candice Hansen, then at the Voyager mission imaging team at the Jet Propulsion Laboratory of NASA. “I was sitting at my desk, reviewing the pictures we had received that day,” says Hansen for OpenMind. In the photographs of the Solar System, the scientist easily identified Uranus and Saturn, but moving the camera towards the inner planets, the effect of the Sun dirtied the images; the presence of the Earth was not obvious. “Then I saw a bright spot in a beam of reflected light, and I quickly got the other two colours to see if it was there, and it was.” “Then I was sure,” continues Hansen. “And that day, and even now as I write these words, a chill runs down my spine. It is so exciting to see our planet from so far away…”
This year, NASA’s New Horizons probe will be the first human artifact to fly over Pluto. It is the mission with the object of study farthest from the Earth until now, but not the most distant spacecraft. Four veterans probes are even today continuing their journeys into interstellar space: Voyager 1 and 2, and Pioneer 10 and 11. The latter two, designed as a kind of rehearsal for the Voyagers, were launched in 1972 and 1973, respectively, and successfully completed their tasks on Jupiter, Saturn, Uranus and Neptune. They continue to travel, although without any contact with the Earth.
The two Voyagers took off in 1977 with the objective of examining the outer planets of the Solar System. Voyager 1, the fastest, overtook Pioneer 10 on February 17, 1998, becoming since then the farthest human emissary from Earth. On August 25, 2012, the probe abandoned the dominions of the Sun to head into interstellar space, a destination that its twin will follow in the coming years. Both are still active and in contact with the Earth. According to the mission’s website in real time, Voyager 1 is already more than 19.5 billion kilometres from the Earth, and its sister, which has surpassed Pioneer 11, is more than 16.1 billion kilometers away.
The four spacecrafts were designed to roam through the universe, in principle forever, since in space they will hardly suffer any deterioration. “There are cosmic rays, gamma rays and so on, but they should remain intact,” says Hansen. And on those trips into eternity, the probes are equipped with messages from Earth, if on their long journeys they should fall into other hands. The Pioneers carry two lead plates with engravings depicting human figures, our location in the cosmos and the path of the probes, all with reference to the hydrogen atom as a universal scale. For its part, the Voyager messages are sonic as well as graphic, images, sounds and music of the Earth; all of it recorded on gold-plated copper phonograph records (needle included), with an analogue technology like the one behind the turntable. These messages can be played in digital format on the website goldenrecord.org.
Sagan was also one of the main driving forces of these messages sent out to infinity. The scientist died in 1996 but his work will survive on this planet and beyond. Hansen emphasizes that in the times of the Pale Blue Dot “the Cold War was still intense between the USA and the USSR.” “We lived with the threat of nuclear war,” she recalls. “I think Carl [Sagan] felt that the mission of the image was to show that we are all together on this beautiful world. Today I think that the meaning of the picture is the same, but we face a different threat, climate change. Today, as 25 years ago, we need to understand that we are all citizens of this planet. It is our only home.”
By Javier Yanes, for Ventana al Conocimiento (Knowledge Window)