Great Expeditions: 50 Journeys that changed our world. Levison Wood

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      An artist’s impression of Voyager 1 entering interstellar space.

      The Apollo 11 moon landing in 1969 captured the public imagination unlike any other space mission in history. However, in terms of furthering our understanding of the Solar System and the galaxy beyond, NASA’s Voyager mission is arguably of far greater significance. Almost 40 years since their launch, the twin Voyager 1 and 2 spacecraft are now further away from Earth than anything else mankind has ever constructed, some 20 billion km in the case of Voyager 1. Their primary mission was to fly by Jupiter and Saturn and send back data that would ultimately re-write astronomy text-books. However, the mission has become far more successful than could ever have been imagined at the outset.

       Interplanetary slingshot

      In 1964, Gary Flandro was working at the NASA Jet Propulsion Laboratory and was given the task of examining ways to explore the outer planets. During the course of his study, he discovered a rare alignment of the outer planets that occurred just once every 175 years. This alignment would allow spacecraft to travel from planet to planet, utilizing their gravitational pull and thus accelerating them out into deep space. Instead of taking forty years, the mission duration could be reduced to less than ten.

      Voyager 2 was the first spacecraft to be launched from Cape Canaveral in August 1977, followed by Voyager 1 a few weeks later. On board were an array of instruments including video cameras, magnetometers, plasma detectors, infrared and ultraviolet sensors, and cosmic-ray and charged-particle sensors. Most intriguingly though, gold records were also attached to the side of each spacecraft. Each disk contains scenes, greetings, music and sounds of the Earth. These include 115 images and a variety of natural sounds such as those made by whales, birds and other animals. There are recordings of the wind, thunder and surf crashing on a beach. There are greetings in fifty-five different languages and a selection of music ranging from Mozart to Chuck Berry’s Johnny B Good. One day, it is hoped that this record of humanity and Earth will be found by some distant intelligent life-form. In reality though, it would be comparatively less noticeable in the vastness of space than a single grain of sand on an ocean beach. Nevertheless, it was a clever public relations move and ensured global media coverage of the mission.

      Both spacecraft have a Golden Record attached to them.

      The super-sized storm

      On March 3, 1979 Voyager 1 reached Jupiter, flying by the giant gas planet some 200,000 km above the planet’s cloud tops. Voyager 2 passed by a few months later. Although Jupiter had been studied for centuries from Earth – most famously by the Italian astronomer Galileo – scientists were surprised by many of the Voyager findings. Voyager’s cameras recorded videos of the Great Red Spot, which is 3.5 times larger than Earth and which was found to be a complex storm that moved across the planet in a counterclockwise direction and has been raging for centuries.

      The most unexpected discovery at Jupiter was on the innermost of its four large moons, Io. Here, for the first time, active volcanoes were seen on a body in the Solar System, other than on Earth. The plumes of which reached 240 km (150 miles up), high enough to hit passing satellites. These volcanoes are thought to be caused by the gravitational tug of war between Jupiter and two of the planet’s other nearby satellites, Europa and Ganymede. This discovery fundamentally changed our opinion and increased our interest in the moons orbiting other planets. Voyager 2 also revealed fascinating details about Europa. This moon’s surface is a thick crust of ice, laced with vivid lines and streaks that may indicate that minerals from below the surface have penetrated the ice. Europa’s conditions could possibly support alien life, albeit in the form of single-celled microorganisms.

       An artist’s impression of the Voyager spacecraft – as well as those from the earlier Pioneer mission – at the edges of our Solar System.

      Unlocking the secret of the rings

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