by Alan Stern
Eighteen months later, that second master’s in hand, Alan moved to Colorado to work as an engineer on NASA and defense projects for aerospace giant Martin Marietta. But after eighteen months he left for the University of Colorado, where he became project scientist (chief assistant to the project leader, which NASA referred to as the principal investigator) on a space-shuttle-launched satellite to study the composition of Halley’s Comet during its once-in-a-lifetime, 1986 appearance. While there he also worked on suborbital science missions and led an experiment to be launched six times on the space shuttle to image Halley’s Comet from space—his first instrument as principal investigator.
But as all this was taking place, Alan wondered just how far he could get in this business without a Ph.D. Already married and with a house and a career, he thought he might have missed that boat by not having chosen the doctoral route back at the University of Texas.
Then, in January 1986, tragedy struck. The space shuttle Challenger exploded seventy-three seconds after launch, killing its seven astronauts. The explosion also destroyed both projects Alan had been immersed in the previous three years: the satellite to study the composition of Halley’s Comet and his first PI experiment—to image Halley’s comet. Beyond the destruction of both his own projects, many of NASA’s other plans were also shattered, and the shuttle’s future was in doubt.
Nearly everyone involved in space exploration back then remembers where he or she was when the shuttle exploded, and some of us still get teary-eyed thinking of Christa McAuliffe, NASA’s first “teacher in space” and the others who lost their lives that cold morning in Florida. Many of us were watching the launch live on TV; Alan was at Cape Canaveral with colleagues, watching the launch.
Following the explosion, Alan was devastated. “You couldn’t escape it anywhere on TV or the papers. For weeks, even months, I just kept seeing that explosion over and over again in the media.” The experience caused him to rethink where his life and career were headed. NASA’s next two planetary missions, Magellan to Venus and Galileo to Jupiter, both orbiters which were supposed to launch on the shuttle, were temporarily shelved. So were virtually all of NASA’s other science missions. Concluding that nothing much new would be happening in space exploration until the end of the decade when the shuttle would fly again, Alan decided to go back to graduate school and get that Ph.D.
So Alan entered an astrophysics Ph.D. program at the University of Colorado in January 1987, exactly one year after the Challenger explosion. There he did his dissertation research on the origin of comets. But Pluto had touched his life. It had provided his first real taste of scientific research, and he did start to wonder, even in graduate school in the late 1980s, about the possibility of sending a dedicated mission there. Why hadn’t NASA thought more about that?
Alan also realized that, by taking a somewhat circuitous route to a Ph.D., he had fallen a few years behind his peers who had pushed straight through. Others his same age had graduated or been in grad school in time to be involved in the excitement of the Voyager project. Had he missed out on the last opportunity to explore new planets for the first time? Not if he could be involved in a mission to Pluto.
When he first raised the matter with senior planetary scientists, the response was not encouraging. Alan:
I think I’m different from most people in our field in the extent to which I’m really inspired by exploration itself, independent of the science. When I was working on my Ph.D., I first started floating the idea of a Pluto mission, saying “We learned so much at Neptune. Why don’t we do a Pluto mission?” It was disappointing to me to learn that senior scientists insisted that a mission to Pluto wasn’t justified simply for its exploration value.
Right there, Alan encountered a basic disconnect between the way NASA actually makes exploration decisions, and the way its efforts are often portrayed to the public. When NASA does public outreach, it often stresses the excitement and intrinsic value of exploration. It’s all about “We are boldly going where no one has gone before.”
But the committees that assess and rank robotic-mission priorities within NASA’s limited available funding are not chartered with seeking the coolest missions to uncharted places. Rather, they want to know exactly what science is going to be done, what specific high-priority scientific questions are going to be answered, and the gritty details of how each possible mission can advance the field. So, even if the scientific community knows they really do want to go somewhere for the sheer joy and wonder of exploration, the challenge is to define a scientific rationale so compelling that it passes scientific muster.
Alan remembers how, in the late 1980s, “Somebody much more senior told me, ‘You will never sell going to Pluto to NASA as exploration. You have to find a way to bring the scientific community to declare it is an important priority for the specific science that such a mission will yield.’”
DISCOVERING PLUTO—1930
Of all the classically known planets, Pluto was not just the farthest and the last to be explored, it was also the most recently discovered—within the lifetime of many people who are still alive. Its discovery in 1930 by Clyde Tombaugh, a Kansas farm boy with no formal technical training, is a classic tale of stubborn perseverance leading to a big payoff.
Clyde, born into a hardscrabble Illinois farming life in 1906, grew up fascinated by thoughts of other worlds. “One day, while in sixth grade,” he wrote in an autobiographical sketch, published in 1980,1 “the thought occurred to me, What would the geography on the other planets be like?” As he grew up, his family moved to a farm in Kansas, where he studied the sky diligently with a 2¼-inch telescope his dad purchased for him from the Sears, Roebuck catalog. He studied astronomy on his own, grinding lenses to build new telescopes and making careful drawings of the markings he observed on Jupiter and Mars. He read everything he could find in the local library relating to astronomy and planets, and he followed the debates about the controversial “canals” on Mars “discovered” and promoted by the wealthy and charismatic Boston astronomer Percival Lowell. He also read about Lowell’s prediction of an undiscovered planet beyond the orbit of Neptune.
Lowell had carefully examined Neptune’s orbit and concluded that some irregularities in its motion betrayed the slight gravitational pull of a distant ninth planet. Clyde read about the observatory Lowell founded on a mountain above Flagstaff, Arizona. He fantasized that he, too, might someday go to college and become an astronomer, but his life felt many worlds apart from all that. Times were not good, and he couldn’t imagine his family ever having the money for him to leave the farm and pursue these dreams.
Still, ever hopeful, he mailed some of his best sketches of Mars to the astronomers at Lowell Observatory. One day in late 1928, to his amazement, he got a letter back from the observatory director, Dr. Vesto Slipher. They were hiring an assistant and wanted to know if he was interested in the job.
You bet he was! In January 1929, with little more than a trunk full of clothes and astronomy books, and some sandwiches his mother had made him for the journey, Clyde boarded a train west, to Arizona. Three weeks shy of his 23rd birthday, excited but a little sad to be leaving the family farm, he watched the scenery change from flat Kansas farmland to dry desert to pine-filled forests as the train chugged out of Kansas and up into the Arizona mountains. That train also carried him—though he didn’t know it—into history.
When Clyde arrived he learned he’d been hired to use the brand-new thirteen-inch telescope to renew the search for “Planet X.” In this amazing assignment he would be taking up a quest that had been started by the famous Percival Lowell. Lowell had died in 1916 without ever finding this prey; now it was Clyde’s job to resume the search.
The new telescope built for hunting down Planet X was better than what Lowell himself had used, and the observatory’s location, at seven thousand feet in the northern Arizona mountains, provided dark, dry skies. The search work assigned to Tombaugh was painstaking. He spent night after nigh
t in the unheated telescope dome throughout the icy winter, taking photographic plates, one after the other, each of tiny portions of the sky in the region where orbital calculations predicted the new planet might be.
The planet Clyde was looking for was expected to be so faint (thousands or even tens of thousands of times fainter than the eye could see), that each photographic plate had to be exposed for more than an hour, while he guided the telescope carefully to compensate for Earth’s rotation and to keep the stars stationary in the frame. Each frame was studded with thousands of stars, occasional galaxies, and many asteroids, and even occasionally comets.
How would Clyde even know that any given point of light was a planet? The key was photographing the same little spot for several nights in a row to detect his faint prey moving against the stars at just the right rate to indicate it orbited beyond Neptune. To analyze the images, he used a device, state of the art at the time, called a “blink comparator” that let him flash between images from successive nights. The background stars would remain still as he blinked between frames, but a planet would show movement.
It’s hard to really overstate how tedious and demanding this must have been. Today every part of this work would be done by computer, but it was all done manually back then. So Clyde went to the telescope every night when the weather permitted and the full moon was not washing out the deep darkness. He lived by the twenty-eight-day lunar cycle, using the downtime afforded by the full moon, when the sky was too bright to photograph the sky for his faint, hoped-for planet, to develop the prints and laboriously examine them, blinking between frames to check first one spot and then the next.
Success was far from guaranteed. Some senior colleagues told him that he was wasting his time; that if there were any more planets, they would have already been found in previous searches. No wonder Clyde suffered bouts of low morale and self-doubt. But still he kept going.
After nearly a year of arduous hunting, on January 21, 1930, the sky was clear and, in his systematic sweep across the sky, his search took him into an area within the constellation of Gemini, the “twins.” It turned out to be a horrible night because of an intense wind that came up, shaking the telescope and nearly blowing the door off the hinges. The images he took were so blurry that they seemed useless, but it turned out that—though he didn’t know it at the time—Clyde had actually photographed his long-sought target, Lowell’s Planet X.
Because the weather conditions on the twenty-first had been so poor, Clyde decided to photograph the same region again on January 23 and 29. It was a good thing he did.
A few weeks later, on February 18, when the nearly full moon once again made searches for faint targets impossible, he set to work blinking between his January images, looking for something that moved at just the right rate to indicate it was at a greater distance than any of the known planets. He had found, by trial and error, that alternating back and forth between the frames at a rate of about three times per second worked best. On one of his January plates, he saw something that matched what he was looking for. A faint, tiny speck was dancing back and forth by about an eighth of an inch—just the right amount to be out beyond Neptune. “That’s it!” he thought to himself. Clyde:
A terrific thrill came over me. I switched the shutter back and forth, studying the images.… For the next forty-five minutes or so, I was in the most excited state of mind in my life. I had to check further to be absolutely sure. I measured the shift with a metric rule to be 3.5 millimeters. Then I replaced one of the plates with the 21 January plate. Almost instantly I found the image 1.2 millimeters east of the 23 January position, perfectly consistent with the shift on the six-day interval on the discovery pair.… Now I felt 100 percent sure.2
At that moment, Tombaugh knew he had bagged his quarry. He also knew that he was the first person to discover a new planet in decades.3 That minuscule pale dot, hopping back and forth like a flea on a dark plate surrounded by a forest of stationary stars, was the first glimpse of a place never before spotted by human eyes.
There was another planet out there! And for a few long minutes, Clyde Tombaugh was the only person on Earth who knew. Then, sure of his find, he walked slowly down the hall to tell his boss. As he stepped down the corridor, he weighed his words. In the end, he walked into the observatory director’s office and said, simply, “Dr. Slipher, I have found your Planet X.”
Slipher knew how careful and meticulous Clyde was. Clyde had never made such a claim before, and this was not likely to be a false alarm. After Slipher and another assistant inspected the images and concurred with Tombaugh’s assessment, they agreed with him but resolved to keep it tightly guarded, telling only a few colleagues at the observatory. Meanwhile, Clyde made follow-up observations to further confirm the discovery and to learn more details about what kind of object it was and how it was moving. A false claim would be devastating.
They spent more than a month checking and rechecking on the new planet and its path in the sky, confirming the calculations that showed it was farther out than Neptune. The planet passed every test they had, appearing in every new image and moving at just the right speed. They also spent the month searching for moons around the new planet (they found none) and trying—with a more powerful telescope—to see it as an actual disk, rather than just a point, so they could estimate its size. They could not, which suggested their planet was small.
Finally, sure of their find, on March 13, 1930, which was both the 149th anniversary of the discovery of Uranus and what would have been Percival Lowell’s 75th birthday, they announced their discovery.
In no time at all, the sensational news spread around the world. The New York Times ran the banner headline: NINTH PLANET FOUND AT EDGE OF SOLAR SYSTEM: FIRST FOUND IN 84 YEARS, and the story was run by countless other papers and radio broadcasts.
The discovery was a huge feather in the cap of Lowell Observatory, which soon felt pressure to choose a name for the new planet quickly, before someone else did. Percival Lowell’s widow, Constance, who had previously engaged in a ten-year battle to rob the observatory of the endowment her late husband had provided for the planet search, now insisted that the planet be named “Percival,” or “Lowell.” Then she wanted it to be called “Constance,” after herself. Naturally, nobody wanted that, but it was a tricky situation for the observatory, which was still financially dependent on the Lowell family.
Meanwhile, more than a thousand letters arrived suggesting names for the new planet. Some were serious suggestions, based on mythology and consistent with the names of the other planets. Among them were Minerva, Osiris, and Juno. Others suggested modern names like “Electricity.” Still other submissions were bizarre or unlikely: a woman from Alaska sent in a poem to support her contention that the planet should be called “Tom Boy,” in honor of Tombaugh. Someone from Illinois volunteered that the planet ought to be named “Lowellofa,” after Lowell Observatory in Flagstaff, Arizona. And a man from New York suggested “Zyxmal,” because it was the last word in the dictionary and thus perfect for “the last word in planets.”
But it was Venetia Burney, an eleven-year-old school girl in England, who suggested the name “Pluto,” after the Roman ruler of the underworld. Her grandfather mentioned Venetia’s idea to an astronomer friend, who in turn sent a fateful telegram to Lowell Observatory, saying:
Naming new planet please consider Pluto, suggested by small girl, Venetia Burney, for dark and gloomy planet.
Clyde and more-senior astronomers at Lowell liked the name and proposed it to the American Astronomical Society and the Royal Astronomical Society of England, both of whom also liked it. The Lowell astronomers thought that the name “Pluto” was perfect, not only because it fit with the convention of naming a planet after an appropriate classical deity, but also because the first two letters in Pluto were PL, which could also serve to honor their founder and benefactor: Percival Lowell.
2
THE PLUTO UNDERGROUND
THE PLUTOPHILES
With the advent of actual planetary exploration in the 1960s, the planets, once merely points of light glimpsed vaguely through telescopes, became real worlds to be reconnoitered and studied with powerful new tools and techniques, including many borrowed from the study of our own home planet, the Earth. Planets have rocks and ice, landforms, weather, clouds, and climate. So the effort to figure out the planets drew in geologists, meteorologists, magnetospheric experts, chemists, and even biologists. Given its complexities, it especially attracted adventurous scientific types who were up for novel interdisciplinary challenges. In the process, a new and distinct field was born: planetary science.
Of all the planets, Pluto—the farthest and the hardest to reach—remained the most obscure and cryptic, and the most difficult to study. But planetary scientists like observing challenges, and they like puzzles, and Pluto provided plenty of each. There’s a drive in scientists to know, and there’s a drive to contribute to the knowing. And with so many mysteries to attack at Pluto, a determined sub-community of scientific Plutophiles developed. Hungry for new information, they employed the most sophisticated telescopes and other advanced tools to puzzle out what they could from so far away, back here on Earth.
One of the first things discovered about Pluto, with the primitive tools available immediately after its 1930 discovery, was the size and shape of its orbital path, which, compared to any other then-known planet, was both huge and genuinely strange. One thinks of the Sun as unimaginably far away from Earth. And it literally is—93 million miles away. When we hear that, our brains have trouble comprehending this as anything other than a really, really big number. So it is common to use analogies to grasp it, for example reducing the Earth to the size of a basketball puts the Sun at 5.5 miles away! But Pluto orbits at an average distance some forty times farther from the Sun than Earth, which means that on this same basketball-Earth scale, Pluto is located 220 miles away!