National Geographic : 2017 Aug
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 nsofarasweesteemthecreationsthat 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. 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 Timothy Ferris, the producer of Voyager ’s golden record, wrote on dark matter in the January 2015 issue. Story produced in part- nership with HHMI Tangled Bank Studios. 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. PHOTO: JOHN GREGOIRE, NASA/JPL. ALL OTHER IMAGES, NASA/JPL GRAPHIC: MATTHEW TWOMBLY. SOURCE: NASA/JPL Congress didn’t really understand the situation, and quietly went to work de- signing and building two tough, smart spacecraft capable of going all the way to Neptune. Any “life limiting” flaws in the probes’ design were weeded out. The sun sensors in their navigation systems were boosted so they could function out where the sun gets dim. Fuel-saving techniques were developed to keep the mission viable long after it was supposed to end. “We just did it and didn’t talk about it,” recalled William Pickering, JPL’s director at the time. The ruse worked. Once Voyager had proved to be both a scientific cornuco- pia and a globally popular emissary to the great beyond, Congress funded the extended mission that JPL had surrep- titiously been managing all along. The Voyagers paved the way for the Jupiter orbiter Galileo and the Saturn or- biter Cassini that followed, which spent years gathering photos and data before being ordered to incinerate themselves in the planets’ upper atmospheres to ensure that they’d never impact and contaminate a possibly life-harboring moon. Now the Voyagers as well are nearing the end of their scientific life. Their weakening radio signals, currently reporting on the surprisingly complex plasma bubble that surrounds the sun and marks the designated boundary between the solar system and in- terstellar space, are expected to fall silent around 2030, when the Voyagers’ plutonium-powered electrical genera- tors finally falter. Thereafter the Voyagers will func- tion more as time capsules than space- ships. With that eventuality in mind, JPL attached to each probe a copy of the “golden record” that contains mu- sic, photographs, and sounds of Earth for the benefit of any extraterrestrials who might intercept it someday. The records should remain playable for at least a billion years before succumbing to erosion from micrometeorites and the high-velocity subatomic particles called cosmic rays. That’s a long time. A billion years ago, the most complex forms of life on Earth were the tidewater mats of cyanobacte- ria called stromatolites. A billion years from now, the brightening sun shall have begun boiling off Earth’s oceans. Yet the Voyagers will still be out there somewhere, emissaries of a species that dispatched them without hope of return.