Returning from the Antarctic, Apsley Cherry-Garrard described exploration as “the physical expression of the Intellectual Passion.” Exploration isn't just adventuring or trekking, nor is it solely thinking or discovering. It's the fusion of the two.
Over the centuries the character of exploration has evolved. I count three Great Ages of Discovery. The Third, today's, began in the postwar era with a renewed inquiry into Antarctica, before plunging into the deep oceans and soaring across the solar system. The linkage of ocean and space was hard welded for a while; aquanauts paired with astronauts, lunar maria and continental shelves would both be colonized, even Arthur C. Clarke wrote novels of both realms in a kind of fugue. But as the Moon race heated up, the oceans receded in popular attention and space seized the commanding heights of imagination. Hollywood filmed Clarke's 2001, not Dolphin Island.
The Third Age achieved an early climax in Voyager's Grand-Tour mission to the outer planets and beyond, launched in 1977 and now silently zooming through interstellar space. But by the time Voyager 1 reached Jupiter, the American space program was in eclipse. It had put all its eggs in a basket called the space shuttle and then the shuttle dropped. Behind the shuttle was the fantasy of colonization, particularly the ever-alluring mirage of Mars as a New New World.
Over the years the convergence of interests that propelled America's space enthusiasms has unbundled. Science, too, has diverged, many of its disciplines preferring instruments that don't need to cross the solar system. The Hubble Space Telescope was better at discovering new moons than fly-by spacecraft. Exploration can no longer rely on a soft valence with science and off-Earth settlement schemes to justify it. It has its own dynamic, and it has fallen to missions like Galileo to Jupiter, Cassini to Saturn, and New Horizons to Pluto to carry the torch of discovery.
New Horizons shows what has become possible. Each of the Voyager twins had three computers and a capacity of 16,000 words, and they recorded data on a magnetic tape; a cheap digital watch today has more high tech and as much power. Yet the massaged photos from Io, Saturn, and Triton set the gold standard for gobsmacking images of discovery. New Horizons packs more punch. Its crisp photos could have been taken over a backyard fence. They reveal not only a strange world, but a fully realized one.
New Horizons is an artifact of our age, and it speaks to what is needed to explore the yet-unvisited shorelines of space, and what such endeavors cost. Most exploration in the coming decades will focus on the deep oceans—those on Earth, not on Enceladus or Europa. Robotic expeditions to the deep are multiplying. They will be far cheaper and more productive, as generators of science, than probes through the icy crust of a Saturnian moon. If all we want is information, Earth-bound science may do, and it can come from a lab more easily than an abyssal plain, much less a planetoid 750 million miles distant.