Voyager: Exploration, Space, and the Third Great Age of Discovery

by Stephen J. Pyne

  Far from being abiotic vats, only capable of supporting life at the surface, the oceans are the dominant habitat on Earth. However hostile to terrestrial life, the sea is an abode for earthly life and is continuous with it. Increasingly it appears that the rifts, submarine volcanoes, hot vents, and black smokers that parse and stitch the solid floor of the sea are fundamental to a grand geochemical cycling of planetary water, and with it the nutrients and minerals essential to a living planet. Not least, it is possible to step from land to sea and back again. The shore is a familiar boundary between the two, literally ebbing and flowing with the rhythms of earthly existence.206

  The void of deep space is a vacuum. Nothing lives within it. It may be that organic molecules travel through the void within particles blasted off planets, but there is no ecosystem possible, and no connectivity between those spores or bio-shards and a Gaian Earth. Passage between planetary bodies is a mix of tiny violence and immense void; the fiery impact of meteorites or the flame-powered launch of rockets. The solar system may loosely resemble Earth, with its interplanetary space assuming the role of oceans, the planets that of continents, and planetary moons as islands. But contact between them requires years of travel across a vacuum. It demands power; and behind power, will; and behind will, belief. One can jump into the ocean by stepping into the surf, but into space only by a leap of faith.

  Another continuity is historical. The oceans have led each age of discovery. The exploration of the world ocean virtually defined the First Age. The Second began with that outrush of circumnavigators of which James Cook, Louis-Antoine de Bougainville, Alejandro Malaspina, and Thaddeus Bellingshausen are its informing captains, and which ferried the fabled naturalists of the era, from Humboldt to Joseph Hooker, to their destinations, and made islands into scholarly ports of call. The age even attempted to extend its powerful Enlightenment science to the sea, making it an object of inquiry and not simply a means of transport. Matthew Fontaine Maury’s Physical Geography of the Sea (1855) adapted Humboldtian techniques to map the oceans. A century after Cook, as the Second Age was completing its final continental traverses, the Challenger expedition applied the accumulated lessons of the Second Age to a global survey of the world ocean, even as its mountainous efforts seemed to yield a molehill of fresh science. Other nations followed, sporadically, with outcomes that seem impressive mostly in retrospect. 207

  The Third Age commenced seriously in the oceans. After World War II, naval vessels were commissioned as research ships and began mapping the solid floor of the world’s seas. Submarines replaced capital ships as nuclear-armed Poseidon missiles became one leg of the American strategic triad; the need grew to know better how to navigate the deep oceans and to communicate with undersea vessels. By the time of IGY, the USS Nautilus and Skate had surfaced at the North Pole, the Trieste was bobbing in the Mediterranean, the Mid-Atlantic Rift was rudely mapped, and it was apparent that the deep oceans were not the lifeless chemical tombs and geologically inert sinks early research and prevailing theory had indicated. By 1962 Harry Hess had published his “History of Ocean Basins,” which inverted the standard geophysical model of Earth, and conceptually catalyzed what became the theory of plate tectonics within a handful of years. No less than comparative planetology, oceanography became a cold war science. As the space race heated up, the U.S. Navy found a desperate need for submersibles and poured money into their development. The Alvin became the naval counterpart to Apollo. The deep oceans were the first of the Third Age landscapes to be mapped, and the one that catalyzed a scientific revolution.

  Not least is the similarity of debates about purpose, especially the wedge issues of human versus robotic exploration, and the ultimate vision of colonization beyond Terra. On this the oceans once again appear to lead. Costs, dangers, the relative merit of human senses versus instruments, the diminishing value of a human brain and hand on board are all propelling deep-sea exploration toward remotely operated vessels or even autonomous submersibles that can wander for weeks. The only sense available to an aquanaut, as to an astronaut, is sight, which is replicated with a richer spectrum by instrumented cameras. The pilot of the Alvin, Robert Ballard, a pioneer of submersibles, having used both crewed vehicles and robots for decades, has concluded that “the robots are better.” So, too, early prospects for a frontier of ocean settlement died in the depths. Ocean exploration can advance unencumbered by techno-utopian colonizers and aspiring homesteaders.208

  After roughly sixty years, the evolving contours of the Third Age suggest that the solar system will not be the primary arena of discovery, that the pattern of exploration among the planets will more resemble the pattern of exploration of the First Age, when complex armadas undertook long voyages, an era of relatively few expeditions but huge returns. Rather, the deep oceans will likely claim the variety and vivacity of exploring, perhaps even the swarm effect that characterized the Second Age. But if so, why does “space” continue to claim pride of place?

  Secrecy is one reason. Much of the oceanic work had military sponsorship and was not broadcast. Nor was there any overt, broadcast-over-TV, soap opera drama for an abyss race as there was for a space race. There was no literature for deep sea exploration as there was for planetary. Robert Heinlein did not write a novel titled Submarine Troopers, nor Ray Bradbury a West Mariana Basin Chronicles. Arthur C. Clarke did not imagine Childhood’s End happening on the East Pacific Rise. Stanley Kubrick did not film 2001: A Sea Odyssey or place alien obelisks on the Valdivia Abyssal Plain. There was no Tsiolkovsky or Goddard to imagine a Great Migration to the Laurentian Abyss, or a Percival Lowell to sketch the contours of a dying civilization on the Loihi Seamount. There was no Carl Sagan to fantasize about cosmic connections with galactic intelligences, or rhapsodize about chemo-spiritual liaisons with “salt stuff ” shared between people and black smokers.

  Over and again, the most publicly ardent proponents of planetary exploration said they saw their endeavor as part of a larger mission to colonize, and an astonishing number traced their enthusiasm to an adolescent literature of technological romance in which worlds were found and lost in space. While the oceans had their lore, and champions of the sea held fiercely to their distinctive sagas of exploration, that tradition stayed on the surface. The utopians wanted colonies on other worlds, by which they meant worlds that looked like planets. What the deep oceans showed, however, was that exploration was neither confined to space nor defined by it. Geographic exploration and space occupied separate cultural realms, though they could from time to time intersect.

  The deep oceans will likely claim the lion’s share in terms of numbers of Third Age expeditions and discoveries. The yet-unvisited oceans may reveal more animals than the terrestrial Earth, answer fundamental queries about the origin and character of life, and tell us more directly than analogies to Mars or Europa about how to care for an abused Earth. But neither numbers alone nor the robustness of oceanographic science can determine cultural clout. Space will retain its partisans, and its promise, and it will offer in the prospects of a sweeping journey, a trek beyond, something that the deep oceans cannot. And that distinction may explain why abyssal exploration has failed to imaginatively inform the coming age. It lacks a Grand Tour. It lacks a Voyager.

  DAY 3, 8 30 - 3,949

  18. Encounter: Neptune

  On June 5, 1989, some 42 months after leaving Uranus, and nearly 142 after leaving Earth, Voyager 2 began the end of its Grand Tour.

  This was the sixth time the Voyager team had met a planet, and Voyager 2 would do what it had done at each prior encounter: it would direct its instruments toward a full-body, geophysical scan of the planet and its satellites. But if the scenario had become ritualized, it had lost none of its wild alloy of awe, anticipation, and anxiety.209

  LAST CONTACT

  JPL uplinked the first of new commands that would prepare the spacecraft to do its gamut of tasks. To scan for ultraviolet emissions that might identify atmospheric chemistry. To search for ra
dio signals birthed where Neptune’s magnetic field met the solar wind and for long-wave radiation that could measure more accurately the opaque planet’s rate of rotation. To measure the brightness of the Sun and of select stars pertinent for navigating through near-encounter events. To ready its infrared instruments by turning their flash heater on and then off. To continue, as it had throughout its long trek across interplanetary space, to sample fields and particles, from time to time recalibrating its instruments by rolls and yaws to allow researchers to account for the distorting influence of the spacecraft itself; to commence a series of four occultation experiments. To search for rings and satellites.

  This was what discovery meant in the popular mind: the revelation of new worlds. The Voyager twins had found a covey of moons at Jupiter, Saturn, and Uranus, and there was every expectation Voyager 2 would discover even more exotic moons here at the outer fringes of the solar system. So its cameras imaged each side of Neptune, and in early July, Voyager found its first new satellite, unimaginatively dubbed 1989N1. This discovery gave the navigation team the needed coordinate by which to guide Voyager through near-encounter maneuvers. Other satellite discoveries soon followed. By the end of the month, Voyager had detected four new moons, subsequently named after figures from Greek mythology—Proteus, Larissa, Galatea, and Despina. On July 30 it captured all four in a single, mesmerizing image.

  On August 6, Voyager 2 left its observatory phase behind and raced toward full encounter. A world that before Voyager had no sharper identity than that of a hazy blue Smurf ball, the third largest of the planets now beckoned at 67,000 kilometers per hour.

  Everything began to surge. Commands—three new computer packets were uploaded. Imagery—Neptune was now too large to fit within a single aperture, so mosaics became the norm. Data—the extra antennas enlisted by the DSN came into play. Less than a day into far-encounter, the last dress rehearsal, a complex execution for an occultation experiment dubbed Radio Science ORT-4, ran for ten hours and identified soft spots in performance, which were quickly corrected.

  The expected discoveries acquired their rhythm. The mosaics were assembled into movies of Neptunian weather; the search for moons intensified; rings, ring arcs, and shepherd satellites came into focus; IRIS recorded temperatures; PRA and PWS tracked radio waves, emitted where Neptune’s magnetosphere met the solar wind. As Voyager 2 quickened its pace, estimates of the planet’s hard parameters sharpened. “The uncertainties that everyone fussed over for so many years,” Charles Kohlhase noted, were “dropping precipitously.” Neptune’s mass and position would be known three times more accurately, Triton three to six times better, and Voyager 2’s time of arrival a third better. The Voyager staff would no longer find Triton’s mass “a mystery.” With the new data, engineers refined parameters for the final, complex roll-turn course correction that would climax near-encounter. Everyone waited for bow shock, the final hurdle before closest approach. It arrived on August 24, 1989.210

  From August 24 to 29, an aging Voyager 2, now zipping at more than 71,000 kilometers per hour, hit its target trajectory, performed a riot of acrobatic maneuvers, amassed mountains of data, and executed nearly 90 high-priority optical and remote-sensing observations. At 8:56 PDT on August 24, Voyager passed within 29,240 kilometers of the planet’s center .211

  It photographed the surface and its wild weather. It sped through Neptune’s ring plane and behind the gaseous giant, sending and receiving radio signals vital for occultation experiments. It used the star Nunki (δ Sagittarii) to occult the rings. It photographed the rings and arcs directly on both approach and departure, as illuminated on the foreside and as backlit, and merged those images into movies. It measured particle impacts. It flew over the north pole of rotation, recording auroral emissions and identifying the magnetic pole. It absorbed the soft geography of Neptune’s ionic and electromagnetic fields, mapping the spongy borders of the magnetosphere. It measured the brightness, pressure, temperature, chemical composition, and cloud structure of the planetary atmosphere. Just before periapsis, Triton occluded the star Gomeisa, and then the Sun, and Voyager seized both opportunities to add to its inventory. Then, while in Neptune’s shadow, it reversed its instruments and surveyed the planet’s dark side. Some 110 minutes after closest approach, Voyager undertook a series of pitches and yaws, realigning from Canopus to Alkaid as a navigational referent in order to position its instruments to interrogate Triton. Relying on image motion compensation, it proceeded to create a high-resolution mosaic of the satellite’s surface. At 2:10 PDT on August 25, Voyager 2 made its closest approach to Triton, some 39,800 kilometers from the moon’s center.212

  The Triton flyby—much sought by scientists—took Voyager 2 out of the plane of the Sun’s ecliptic, and hurled it obliquely southward at forty-eight degrees. With that effort, Voyager had shot its bolt: it would encounter no further worlds. In fact, the odd trajectory actually caused a gravity-assisted slowdown. Some thirty-eight hours after entering bow shock, Voyager exited the magnetosphere, and continued to move in and out of bow shock amid the filmy fields for another two days. Finally, seventy-nine hours after closest approach, it turned its cameras back to the planet and its moon.213

  The gesture had become a valued parting ritual begun by Voyager 1 when, hurrying to Jupiter, it had turned and captured Earth and the Moon in a single image. This time Voyager caught the double crescents of Neptune and Triton in an unforgettable scene: haunting, austere, radiantly lonely. It was the Grand Tour’s last work of art.

  Post-encounter had its usual anticlimactic aura—“like the cleaning crew that does its work the morning after an all-night party,” Ellis Miner thought. The phase began officially on August 29 and didn’t end until October 2, 1989, almost exactly thirty-two years after Sputnik 1 launched.214

  This time post-encounter did not have the anxieties attendant on the need to target another planet. But Neptune’s remoteness added an anxiety of its own. The immense distance, low wattage, and feeble computing capabilities meant that much of what Voyager 2 had sensed it still had to send to Earth. Its digital tape recorder had to play back the drama of near-encounter. It did so twice in order to reduce noise, fill gaps, and substitute redundancy for lost transmitting power. Even so, critical instruments continued to record and image. The far side of Neptune had its interests and its partisans, and the fields of soft geography busily reclaimed the place they had temporarily yielded to hard geography. Then the spacecraft undertook a final series of rolls and yaws to recalibrate instruments and navigational systems before beginning its final, uninterrupted cruise to infinity. 215

  TRITON

  Triton was the last of Voyager’s surveyed worlds, and with a fitting sense of closure, perhaps the strangest.

  Almost everything about Triton proved exceptional. It combines variety with size. It has “perhaps the most diverse geological land forms found anywhere in the Solar System,” the result of a complex and dynamic history. It has an atmosphere flush with ices of nitrogen, methane, carbon monoxide, carbon dioxide, and water. Among icy satellites, it has the “most spectrally diverse surface.” It is the seventh largest moon, with a volume more than five times that of Titania (the eighth largest), but it is the only large satellite with an inclined, retrograde orbit, an orbit almost perfectly circular. Unlike other captured moons, it shares no features with asteroids; it more closely relates to objects from the Kuiper Belt and best resembles Pluto. How it originated—whether by capture or by co-evolution with Neptune or whether it might share some eccentric history with Pluto—is at present indeterminate. What is known is that Triton is the coldest body identified in the solar system, a scant thirty-eight degrees Kelvin above absolute zero.216

  That made the discovery of geologic activity astounding. Studying images revealed what appeared to be transient streams or plumes of gas. In all, Voyager 2 photographed four eruptions—nitrogen geysers—that lofted emissions some eight kilometers high before shearing winds carried them one hundred kilometers beyon
d. The proposed explanation was that insolation, however feeble (900 times lower than on Earth), could still penetrate Triton’s clear icy cap, create a greenhouse effect underneath, and build up a gaseous pressure that then vented violently back to the atmosphere.217

  The scene offered a fitting sense of closure: the cold eruptions on Triton bracketed the hot ones on Io. The unforeseen discovery of volcanoes on Jupiter’s Io had announced convincingly that Voyager would find new worlds, and now at the end of its trek, one had come to expect the unexpected. At Triton the Grand Tour’s alpha had found its omega.

  INFORMATION AND IDEA

  That was what the Third Great Age of Discovery had done overall. Not only had it revealed unknown lands but it had intellectually remade an Earth that many believed already discovered and old. Like the First Age, it had found new lands, and like the Second, it had seen old lands with new eyes. Knowledge, after all, was relative. It was contingent not only on fresh data but on novel means of interpreting.