National Geographic : 2017 Aug
DEEP IN SPACE, TWO INTREPID TRAVELERS TURN 40 Launched in August and September 1977, NASA’s twin Voyager spacecraft have opened up new worlds for exploration, including Saturn (top) and Jupiter, Uranus, and Neptune (above, left to right). | EXPLORE | FANTASTIC VOYAGE SPACE CURRENT DISTANCE FROM THE SUN Billions of miles 12.9 10.6 Sun VOYAGER 1 Launch: September 5, 1977 VOYAGER 2 Launch: August 20, 1977 Jupiter March 5, 1979 July 9, 1979 Neptune August 25, 1989 Uranus January 24, 1986 Saturn November 12, 1980 August 25, 1981 Mercury, Venus, and Mars omitted for clarity August 2012 Voyager 1 leaves heliosphere, enters interstellar space The prospect of a “grand tour” of the outer planets emerged in 1965 from the musings of an aeronautics graduate stu- dent named Gary Flandro, then work- ing part-time at NASA’s Jet Propulsion Laboratory in Southern California, the world’s preeminent center for interplan- etary exploration. At age six, Flandro had been given Wonders of the Heavens, a book that showed the planets lined up like stepping-stones. “I thought about how neat it would be to go all the way through the solar system and pass each one of those outer planets,” he recalled. Assigned at JPL to envision possible missions beyond Mars, Flandro plotted the future positions of Jupiter, Saturn, Uranus, and Neptune with paper and pencil. He found that they would align in such a way that a spacecraft could tap the planets’ orbital momentum to slingshot from one to the next, gaining enough velocity to visit all four planets within 10 or 12 years rather than the decades such a venture would require otherwise. The mission launch window would open for a matter of months in the late 1970s, then close for another 175 years. It was an ambitious idea at a time when the apex of interplanetary explo- ration was Mariner 4 shooting 21 grainy photos as it flew past Mars. No probe had ever functioned for anything close to a decade in space. None had the intelli- gence to manage complex planetary encounters at vast distances without constant human hand-holding. Playing crack-the-whip past multiple planets might work in theory but had never been attempted in practice. “I was told, ‘This is impossible; stop wasting my time,’” Flandro recalled. NASA swallowed hard and proposed a grand tour mission anyway, but Congress rejected it, instead approving a cheaper, stripped-down version that would ven- ture out no farther than Saturn. The JPL spacefarers responded in the tradition of the hardiest explorers of earlier epochs. They cheerfully agreed to the plan, assured one another that By Timothy Ferris I nsofar as we esteem the creations that last—Homer ’s Odyssey, the bridge still standing, enduring love—let us now praise the twin Voyager space probes, launched 40 years ago and currently departing the solar system to drift for- ever among the stars. Each about the size and weight of a subcompact automobile, the Voyagers epitomize 1970s high tech. Their com- puters are weaker than those in today’s digital watches, their analog TV cameras more primitive than the ones that shot Laverne & Shirley. But they made history at every planet they reconnoitered— confirming, as Voyager chief scientist Ed Stone put it, that “nature is much more inventive than our imaginations.” Jupiter, which looks serene through a telescope, was shown by Voyager to have hundreds of raging hurricanes, a glow- ing aurora at the north pole, and three thin rings. Saturn’s rings, previously countable on the fingers of one hand, turned out to include thousands of ring- lets and seemingly braided components that theorists had assumed were im- possible. (“We thought we knew it all,” said astronomer Brad Smith. “Ha!”) Active volcanoes, formerly found only on Earth, turned up in abundance on Jupiter’s satellite Io and, astoundingly, on Neptune’s Triton, where nitrogen geysers were observed erupting at 40 degrees above absolute zero on the Kelvin scale. Two of the solar system’s most promising environments for find- ing alien life—Jupiter’s icy moon Europa and Saturn’s Enceladus—were unveiled by the Voyager mission. Their cores pal- pitated and heated by tidal interactions, Europa and Enceladus appear to sustain vast, briny oceans beneath the ice, where living organisms might thrive. A big-science endeavor that con- sumed some 10,000 work-years, the mission has been described as “one of the greatest voyages of exploration ever conducted by our species.” Yet it almost didn’t happen. A Voyager spacecraft undergoes testing at JPL in No- vember 1976, nine months before its launch. Originally built to last five years and explore Jupiter, Saturn, and their moons, the Voyagers are now far beyond Pluto and still sending scientific information back to Earth. THE GRAND TOUR Voyagers 1 and 2 were launched 40 years ago on a mission to ex- plore the outer solar system. After encountering Saturn, Voyager 1 angled upward. Voyager 2 went on to visit Uranus and Neptune before angling downward.