This book tells the story of a small but sophisticated machine that traveled a very, very long way (3 billion miles) to do something historic—to explore Pluto for the first time. It achieved that goal through the persistence, ingenuity, and good luck of a band of high-tech dreamers who, born into Space Age America, grew up with the audacious idea that they could explore unknown worlds at the farthest frontier of our solar system.
The New Horizons mission to Pluto had many roots. They reach back to the astonishingly difficult discovery of Pluto in 1930. They then extend, over half a century later, to the delightful discovery of a host of other worlds orbiting at the edge of our planetary system, and to an underdog proposal to NASA by a determined team of young scientists bent on historic exploration and new knowledge.
Scientists don’t necessarily believe in destiny, but they do believe in good timing. So we begin in 1957, the year that the first spacecraft, called Sputnik, was launched into Earth orbit.
KICKING TO GET STARTED
Sol Alan Stern arrived on Earth in New Orleans, Louisiana, in November 1957, the first of three children born to Joel and Leonard Stern. His parents say it was a very easy pregnancy, except for the final few weeks. Then he suddenly began kicking, like crazy. Alan’s father maintained, years later at his son’s fiftieth birthday party, that Alan had apparently been hearing people talking about the launch of Sputnik, and was clearly impatient to get out and get going to explore space.
Alan grew up interested in science, space exploration, and astronomy, from his earliest days. He read everything he could get his hands on about space and astronomy, but eventually ran out of library books—even in the adult section.
When Alan was twelve, he watched newsman Walter Cronkite on television describing one of the early Apollo landings while holding up a detailed NASA flight plan. “You couldn’t actually read it on TV,” said Alan, “but you could see it ran hundreds of pages and was filled with all kinds of detail, with every activity scripted, minute by minute. I wanted one, because I wanted to know how space flight was really planned. I thought ‘If Walter Cronkite can get one from NASA, then I can get one too.’”
So Alan wrote to NASA, but when told he wouldn’t be receiving a copy because he wasn’t an “accredited journalist,” he decided to double down and fix that issue. Over a year, he researched and wrote by hand a 130-page book. The title was “Unmanned Spacecraft: An Inside View,” which—as Alan is the first to note—was “a pretty funny title for a kid who was entirely on the outside and learning as he went.”
But it worked. Not only did Alan receive a whole set of Apollo flight plans from NASA, he ended up being taken under the wing of John McLeish, the chief NASA public affairs officer in Houston, often heard narrating Apollo missions on TV. In fact, McLeish began sending Alan a steady stream of Apollo technical documents: not just flight plans, but command-module operation handbooks, lunar-module surface procedures, and much more. Alan became hooked on a space career, but knew he’d have to study for a decade to get the technical skills to join the space workforce after college.
THE GRAND TOUR
Around the same time that John MacLeish was befriending him, Alan also got hold of the August 1970 issue of National Geographic, with a cover depicting Saturn as it might appear from one of its moons. The painting, showing the giant, ringed planet cocked at an angle, floating against the black of space over a cratered, icy, alien landscape, seemed at once both realistic and utterly fantastic. The cover story, “Voyage to the Planets,” is something that many planetary explorers of Alan’s age remember paging through as kids. It contained a level of magic—robotic spaceflight—that today would be found in Harry Potter.
The article described how in the decades to come, NASA planned to launch a series of robotic spacecraft that would explore all the planets and transform knowledge of them from science fiction fantasies into actual photographs of known worlds.
The exploration of the solar system was portrayed as an ongoing sequence of journeys. The article was accompanied by profiles of the first generation of planetary scientists—Carl Sagan among them—who conceived, launched, and interpreted the data from those first voyages. By 1970, NASA had managed to launch only seven spacecraft beyond Earth to reach other planets—three to Venus and four to Mars. These first interplanetary crossings had all been “flybys,” missions which simply sent a spacecraft zooming past a planet, with no ability to slow down to orbit or land, gathering as many pictures and other data as possible during a few hours near closest approach. (Note: we say “simply,” but, as the following pages of this book illustrate, there is actually nothing simple about it.)
That National Geographic article described how the 1970s promised to be “the decade of planetary investigation,” with an ambitious list of planned and hoped-for NASA missions that would open up the rest of the solar system to humanity. First, in 1971, would be a pair of orbiters to Mars. Next would be the first missions to the immense uncharted realm of what was then called the outer solar system, as Pioneer 10 and 11 would reach Jupiter in 1973 and 1974 and then travel on to reach Saturn in the distant year of 1979.
Shortly after, Mariner 10 would make the first visit to Mercury, traveling there by way of Venus, where it would make the first ever use of a “gravity assist,” a nifty trick that has since become indispensable for getting around the solar system. In a gravity-assist maneuver, a spacecraft is sent on a near-miss trajectory to one planet, which pulls it in and then speeds it toward its next target. It seems too good to be true—like getting something for nothing, but it’s not—the equations of orbital mechanics do not lie. For the planet, the tiny loss of orbital speed it trades with the spacecraft has no meaningful effect, but the spacecraft gets a whopping shove in just the right direction. Pioneer 11 was slated to use this same trick during its planned flyby of Jupiter, allowing it to then go on to Saturn.
If all these missions were successful, then before that decade was out, spacecraft from Earth would have visited all five planets known to the ancients—Mercury through Saturn. And what’s more, Pioneer 10 and 11, sped up from their close encounters with Jupiter and Saturn, would be racing outward with enough velocity to eventually escape the Sun’s gravitational hold entirely, becoming the first human-built artifacts to leave our solar system (along with their uppermost rocket stages).
And then what? There would still be three other planets left to explore, but at the vast orbital distances of Uranus, Neptune, and Pluto it would take an impossibly long time to reach them. Unless …
The National Geographic article described an ambitious plan to launch a “grand tour” mission that could use multiple gravity assists to visit each of these planets. In theory, a spacecraft could be launched outward toward Jupiter, relayed toward Saturn, and then again relayed successively to each more-distant world. Such a mission would allow all the planets, even distant Pluto, to be reached in less than a decade, rather than the multiple decades such a journey would otherwise take.
But this trick cannot be attempted at any random time, even in any random year or century. The planets, each one on its own orbit around the Sun, need to be arranged in just the right way, like beads strung on an arc, stretching from Earth to Pluto. Like a secret passageway appearing only briefly every couple of centuries, the motions of the planets line up to create such a conduit only once every 175 years.
It just so happened that one such rare opportunity would soon present itself, and it was dubbed the “Grand Tour.” Using it, a spacecraft launched by the late 1970s could quickly travel all the way across the solar system, visiting every outer planet in turn and arriving at Pluto by the late 1980s. It was fortuitous that at that moment in history, in the late twentieth century, when humans had just figured out how to launch spacecraft to other worlds, such a rare chance would be coming around.
There were lessons here for a young reader: The laws of physics can be our friends. They can be used to achieve things that would otherwise be beyond reach. And sometimes things line up just right to provide opportunities that, if not seized, won’t come around again for a very long time.
That National Geographic was illustrated with early spacecraft photographs of Mars and Venus, and artists’ depictions of the planets as yet unexplored. It also contained a table summarizing the known facts about all nine known planets, and one planet stood out from the others as completely mysterious. In the column for Pluto, most of the boxes were filled in with just question marks. Only the details of its vast and distant orbit (taking 248 Earth years to complete one of its own) and its length of day (spinning on its axis once every 6.4 Earth days) were given. Number of moons? Unknown. Size? Unknown. Atmosphere? Surface composition? Both also unknown. There was nothing to give us much of a clue about what it might actually be like on Pluto. Alan remembers reading that article and seeing that table, and thinking about spaceships one day exploring mysterious Pluto, the most distant unknown of all the planets.
VOYAGERS
Back then, most interplanetary missions launched as pairs of spacecraft, to guard against the possibility that one might fail. There was good logic in that, because the cost of building a second, identical spacecraft is much reduced by borrowing the design and much of the planning for the first. For example, Mariner 9, the Mars orbiter that finally revealed the “Red Planet” in all its detail and glory was successful. But its twin Mariner 8 ended up crashed beneath in the Atlantic Ocean due to rocket failure. A similar fate had met Mariner 1, though Mariner 2 made it to Venus, and Mariner 3 had failed, but Mariner 4 got to Mars.
NASA’s planned grand tour of the giant planets included two pairs of identical spacecraft that would visit three planets each. One pair, to be launched in 1977, would fly by Jupiter and then be ricocheted on to Saturn and Pluto. The other pair would launch in 1979 to visit Jupiter, Uranus, Neptune, and Pluto. The grand tour would complete what Carl Sagan referred to as “the initial reconnaissance of the Solar System.”
It was a wonderful plan, but sending four spacecraft to each visit three planets was just too expensive. The projected cost to design, build, and fly this mission, lasting well over a decade and traveling much farther than any spaceflight in history, was more than $6 billion of today’s dollars. Sadly, at that time NASA’s budgets were falling, and in that environment such an expensive mission was a nonstarter. The grandiose grant tour was canceled before it ever got off the drawing board.
Recognizing that the opportunity would not come again in their lifetimes, the science community scrambled to reduce cost and rescue the grand tour, producing a scaled-down version called the “Mariner Jupiter-Saturn” mission, with the more modest goals of exploring only the two largest and closest outer-solar-system planets: Jupiter and Saturn. This twin-spacecraft mission, at just under $2.5 billion in today’s dollars, was approved in 1972. A contest was held to formally name the spacecraft, and they were christened Voyager 1 and 2 just months before their launches in August and September 1977.
Although the original grand tour had been canceled, the Voyager 1 and 2 launch dates and trajectories were cleverly chosen to enable the craft to keep going after Saturn, using gravity assists to reach all the other planets. The nuclear power source was also designed with enough energy to fly the spacecraft for many years after the “primary mission.” So, potentially, these craft could continue on to Uranus, Neptune, and Pluto if funds could later be found to pay for their extended flights.
The Voyager mission would be considered a complete success if it just succeeded in exploring the Jupiter and Saturn systems. Yet its designers planned that—with luck, and future resources they couldn’t count on—it just might be possible to keep it going for years longer and billions of miles farther, completing all of the grand tour’s objectives after all. And indeed, the Voyagers ultimately did just that. Launched in the late 1970s, each completed its primary mission at Saturn by 1981, and both are still operating today—four decades after launch. Voyager 2 traveled in the direction of Uranus and Neptune, but the wrong direction to reach Pluto, but Voyager 1 headed in the right direction.
So why didn’t Voyager 1 go on to Pluto? One of the big prizes, and one of the official metrics for success for Voyager, was the exploration of Saturn’s unique and enigmatic, giant moon, Titan. As the only moon in the solar system with a thick atmosphere, even thicker than Earth’s, and like the air we breathe made mostly of nitrogen, it naturally stood out as a place scientists wanted to know better. Titan also possessed hints of some interesting organic chemistry (the kind of chemistry, involving carbon, that on Earth enables life to exist), and its atmosphere was known to include the carbon-containing gas methane. This had been discovered in 1944 by astronomer Gerard Kuiper, one of the founders of modern planetary science and someone whose name we’ll see again soon.
There was a problem, though, and Titan forced a difficult trade-off. Voyager 1 could only do a really good job of investigating Titan if it made a close flyby immediately after flying by Saturn. Executing such a maneuver would pull the spacecraft permanently off the grand-tour trajectory, flinging Voyager 1 toward the south, veering sharply out of the plane of planetary orbits. This post-Saturn flight direction would make a continuing journey outward to Pluto impossible. At the time, no one could really argue successfully that Voyager 1 should skip Titan. It was a body relatively near at hand compared to Pluto, and scientists knew Titan was fascinating. By contrast, the risky, five-year journey onward to distant Pluto, a body about which so little was known that no one could say it would be worth the effort. Picking Titan over Pluto was a good, and logical, choice. And even today, no one regrets this decision, especially now that Titan has proved to be a world of wonder with methane clouds, rainfall and lakes, and vast fields of organic sand dunes—truly one of the most enticing places ever explored. It was indeed the right decision, but it also closed the door on humanity’s chance for a visit to Pluto in the twentieth century. If Pluto were ever to be visited, it would be left for another time, and another generation.
SCHOOL DAYS
Alan finished college, at the University of Texas, in December 1978. Just as Voyager 1 was approaching Jupiter, in January 1979, he then started grad school in aerospace engineering. His fascination with space exploration continued, but he did not see himself becoming a scientist. Even today he remembers hearing about the decision for Voyager 1 to study Titan rather than attempt the longer, riskier journey to Pluto. “I remember thinking back then, ‘They made a smart choice, but it’s too bad—we’ll probably never have the chance to see Pluto.’”
Alan maintained a keen interest in the way spacecraft missions work, but his master’s program, with a focus on orbital mechanics, was strategically designed to build a résumé that would enable him to be selected by NASA’s astronaut program. What would be the right next move for that?
Alan wanted to show NASA he was versatile, so he went for a second master’s in another field, planetary atmospheres. The choice turned out to be pivotal. Alan recalls:
There was a young, hotshot planetary research professor at Texas who also wanted to be an astronaut, Larry Trafton. He had come out of Caltech and had made some pretty big discoveries. He also had a reputation for rigor and toughness. I remember going to Trafton’s office and knocking on the door and feeling very intimidated by his reputation, but telling him I would work for free if he had any ideas for a project we could do together. He told me about a paper he had just written about Pluto that made some calculations about the behavior of Pluto’s atmosphere and the high rate that it was escaping into space, which indicated that Pluto should have completely evaporated over the age of the solar system. Of course, this didn’t make sense—because Pluto was still there, indicating something else was going on we didn’t understand. Trafton just happened to be puzzling over this when I knocked on his door in late 1980, asking for a good research problem to work on. So he said, “Why don’t you work on Pluto?” and that eventually became my master’s topic. We did some explorations of the basic physics of what Pluto’s atmosphere might be like. Very simple computer modeling by today’s standards, but illuminating for its time.
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 night 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.