Voyager I at the Heliopause
Friday, January 18, 2013
An extension of human ingenuity will soon reach the farthest limit of the sun’s empire. Beyond is true interstellar space.
If you would like to get an idea of how fast the reach of humankind is accelerating, consider this. In 1783, only 230 years ago, the Montgolfier brothers gave a public demonstration of the world’s first practical antigravity device, the hot-air balloon. It reached an altitude of about one mile. And 160 years later, a V-2 rocket, sent straight up, reached 128 miles.
But then in 1977, barely a quarter-century later, NASA launched Voyager I. Today that spacecraft has traveled 11 billion miles from Earth, 85 million times as far as that V-2 rocket of 60-odd years ago. And unlike the Montgolfier balloon and V-2, Voyager will never return to Earth. Until its power source gives out in 15 years or so, it will continue to send data back to the planet from which it is receding at more than 38,000 miles per hour. Then, dark and silent, it will cruise through space for eternity.
At Voyager’s distance today, the sun appears as no more than a point source of light, such as the stars in the night sky appear to us. Of course, it is still a very, very bright point source of light, at magnitude -16.3. That is roughly 40 times as bright as the full moon appears to us.
Voyager has traveled so far that it is now near the heliopause. At the heliopause, the solar wind — the stream of charged particles that emanates from the sun and causes such phenomena as aurorae and the tails of comets — becomes so attenuated that it blends into the interstellar medium. The heliopause, in other words, is the farthest limit of the sun’s empire. Beyond is true interstellar space, the empire of the Milky Way.
The development of the V-2 rocket, like that of the full-rigged ship 500 years earlier, opened a great age of exploration. In 1488, after decades of pushing farther and farther down the coast of Africa, the Portuguese finally reached the Cape of Good Hope at the southern tip. The wonders — and riches — of India and the Far East then lay open to direct European exploration and exploitation.
Interstellar space is so empty and so vast that Voyager will not even reach the distance of the nearest star for more than 80,000 years.
To be sure, there are no material riches to be gained beyond the heliopause, at least as far as anyone knows. Interstellar space is so empty and so vast that Voyager will not even reach the distance of the nearest star for more than 80,000 years. But the knowledge we have already gained from Voyager and other spacecraft has transformed our understanding of the solar system and the universe beyond.
So if knowledge is power, the human race has become vastly more powerful in the last 60 years, thanks to the space exploration carried out by vehicles such as Voyager.
In 1950, our knowledge of the solar system was extraordinarily limited. We didn’t even know such basic facts as the rotation rate of Venus, the nearest planet to Earth, or Mercury. The four big moons of Jupiter, discovered by Galileo in 1610, remained mere dots of light circling the giant planet. They were assumed to be dead worlds not unlike Earth’s moon, which is roughly the same size.
Pioneer 10 had flown by Jupiter in 1972, but it was Voyager I and its partner, Voyager II, that transformed our understanding of the Jupiter system. The two Voyagers discovered the planetary rings, whose existence was quite unexpected. Subsequently, Voyager II would discover the faint rings around both Uranus and Neptune. Rings, in other words, are attributes of all the gas-giant planets, with Saturn’s being just the most spectacular.
The biggest surprise, however, turned out to be the Galilean moons. Far from resembling Earth’s moon, each is unique. Europa, the smallest, is covered with a thick crust of ice that might have a life-bearing sea beneath. Io, the innermost, is greatly affected by Jupiter’s immense gravity. Tidal forces heat the interior and produce volcanoes, the first ever observed beyond Earth. Far from looking like Earth’s moon, Io, in the words of one NASA scientist, looks like “a big pizza.”
After Galileo’s discovery in 1610, no more moons of Jupiter were found until 1892. By the mid-1970s, 13 were known, thanks to ground observation. The two Voyager expeditions discovered three more. Today we know of 67 moons orbiting Jupiter, most of them small and almost certainly captured asteroids.
Voyager I received a gravity assist from Jupiter, speeding up enough to reach escape velocity from the solar system (while, thanks to the law of the conservation of energy, Jupiter slowed down by an infinitesimal amount). But thanks to some careful navigation, it first flew past Saturn, skimming a mere 77,000 miles over the cloud tops.
Until its power source gives out in 15 years or so, Voyager will continue to send data back to the planet from which it is receding at more than 38,000 miles per hour.
Again a cascade of new knowledge resulted. Saturn’s magnificent rings were explored in depth for the first time and their complex dynamics became more understood. Saturn’s big moon Titan, second largest in the solar system and the only satellite to have a thick atmosphere, was explored up close for the first time.
Exploring Titan required that Voyager I change its trajectory. This, in turn, meant that after the encounter with Titan, Voyager I would leave the plane of the ecliptic (within which all the planets orbit the sun) and sail out into space. Voyager II, after exploring Saturn, continued on a path that would eventually take it to Uranus and Neptune. Today, it, too, is headed for interstellar space.
Since the two Voyagers were launched, the spacecraft named for Galileo explored the Jupiter system for years and Cassini still dances among the rings and moons of Saturn. In 2004, Cassini released Huygens, which landed on Titan, revealing a wondrous world of methane rain and lakes. New Horizons, launched in 2006, will reach Pluto and the Kuiper Belt in 2015.
Noel Coward once wrote of his countrymen that, “We will continue to go down to the sea in ships, for ours is an island race.” Today all humankind is an island race and our ships sail ever farther upon the infinite sea of space, sending back cargoes not of “diamonds... cinnamon, and gold moidores,” but of knowledge. It is a cargo more precious by far.
John Steele Gordon has written several books on business and financial history, the latest of which is the revised edition of Hamilton's Blessing: The Extraordinary Life and Times of Our National Debt.
FURTHER READING: Gordon also writes “The Politically Correct Calendar,” “Debt and the Constitution,” and “The Scariest Day of My Life.” Lewis M. Andrews discusses the abandonment of space exploration in “The High Cost of Government Waste.” David Shaywitz contributes “Space: Still Cool After All These Years.” Arthur Herman says “Goodbye, Atlantis.”
Image by Dianna Ingram / Bergman Group