Pluto and Lowell Observatory: A History of Discovery at Flagstaff

INTRODUCTION

The roads by which men arrive at their insights into celestial matters seem to me almost as worthy of wonder as those matters in themselves.

—Johannes Kepler

Several years ago, when someone learned of my association with Lowell Observatory, they immediately said, Pluto should never have been found. Percival Lowell was looking for a ghost, and Clyde Tombaugh found it for him! The association between the observatory, its many-faceted founder and the persistent (and clear-eyed) Kansas farm boy whom he never met is a uniquely American story. The connection between the observatory and Pluto has continued for generations of Lowell researchers and their supporters with the additional discoveries about Pluto and its environs that have occurred.

Pluto has always surprised us. Of course, we have only known of it for just over one-third of a Plutonian year, but in that astronomically short period, it has always been a source of new knowledge, and many times it has upset established understandings. The number of new discoveries surrounding this one body is evidence of how much more there is to learn about the small neighborhood in space we call the solar system.

From the initial searches with their false assumptions, to the nearly immediate recognition that Pluto was different than expected, through the discovery of other Kuiper belt objects, Pluto’s moons and atmosphere, Pluto kept proving to be more than what people expected. The New Horizons mission has only added to this tradition, with its images and data disrupting our current theories and establishing a need to rewrite the textbooks of planetary body formation and activity. The efforts and persistence of those who made New Horizons happen are a modern version of the struggles and challenges the initial discoverers went through—and on about the same timeframe.

Scientists at Lowell Observatory and other research organizations in Flagstaff have been involved in these discoveries and the associated rethinking of planetary evolution. Acquiring new knowledge is never easy and always requires persistence and willingness to accept facts and look for answers that run counter to established theory. For more than a century, Pluto and the efforts to understand it have been teaching us how much more there is to learn and the value of continuing to study and discover. It is an experience likely to be repeated, as our efforts should reveal much more about this surprising body in the next one hundred years. This is both a challenge and an opportunity for all of us, one that is both exciting and daunting. The example set by those in this book who have done so much before us gives us the encouragement to look for more and the anticipation of exciting new discoveries that lie ahead.

W. Lowell Putnam

Sole Trustee of Lowell Observatory

Great-grandnephew of Percival Lowell

CHAPTER 1

AN EXERCISE IN

TRIAL AND ERROR

It means a planet out there as yet unseen by man, but certain sometime to be detected and added to the others.

—Percival Lowell

The year 1902 was a tipping point for a trio of Harvard University graduates whose relationships to one another ranged from close friends to family. The most well known of them was Theodore Roosevelt, who was in the first year of his presidency and leading a countrywide reform movement that included the dissolution of several dozen trusts, regulation of railroad rates and expansion of the United States onto the world scene. Roosevelt would also make his mark in conserving the country’s natural resources, an effort that effectively kicked off with an eight-week trip the following year to the American West. He traveled to such iconic spots as Yellowstone in Wyoming and Yosemite in California. He also went to the Grand Canyon in Arizona, becoming the first president to visit Arizona along the way. Little did he know that, while riding a train through Flagstaff on his way to the Grand Canyon, he passed within the shadows of an astronomical observatory that sat atop a hill overlooking the town. The facility had been founded a decade earlier, primarily for the study of Mars.

One of Roosevelt’s friends at Harvard was Owen Wister, who reached widespread fame in that year of 1902 with his book The Virginian. Like Roosevelt, Wister was fascinated with the American West and dedicated the book to his old pal Roosevelt. This volume would soon become recognized as the prototypical western novel, a classic that became the basis for a play, several films and two television series. Twenty-eight years after publication of The Virginian, a twenty-four-year-old assistant at that observatory on the hill anxiously sat in a movie theater in Flagstaff and watched Gary Cooper starring in a film adaptation of the book. The assistant was desperately trying to keep his mind off the fact that clouds had covered Flagstaff ’s sky that evening in 1930, preventing him from photographing the planet he had discovered earlier that day and culminating a search whose seeds were sown by the founder of the observatory.

Roosevelt had arrived for his freshman year at Harvard in the fall of 1876, just months after one of the university’s most talented mathematics students graduated. His name was Percival Lowell, and while he missed overlapping with Roosevelt at Harvard by those few months, the two would intersect privately—one of Lowell’s sisters married a cousin of Roosevelt, and for a time Percival was engaged to Rose Lee, the sister of Roosevelt’s first wife, Alice.

Lowell founded his Flagstaff observatory in 1894, making headlines with his controversial proclamations about life on Mars. He would leave several astronomical legacies, including his quest to find a ninth planet he believed lurked in the outer reaches of the solar system. He first mentioned this theoretical planet in a public lecture late in 1902. While it ultimately eluded him, his enthusiasm for the search inspired his successors at the observatory, culminating with Clyde Tombaugh’s discovery of Pluto on February 18, 1930.

TO BE A LOWELL

Percival Lowell hailed from one of Boston’s elite Brahmin clans, known for its accomplishments in areas ranging from commerce to academia. The family produced more than its fair share of businessmen, judges, writers, industrialists, ministers, philanthropists and architects. The family motto, occasionem cognosce, means know your opportunity, and family members took this to heart in pursuing excellence. To be a Lowell meant not merely relying on the family wealth to sail through life. Instead, family members were expected to assume leadership roles, whether in their chosen vocation or community activities.

Percival was born in 1855, the eldest of seven children (five survived to adulthood, including two boys and three girls). As Percival’s brother Abbott noted in his biography of Percival, their father instilled in the children the Lowell work ethic: Somehow he made us feel that every self-respecting man must work at something that is worthwhile, and do it very hard. In our case it need not be remunerative, for he had enough to provide for that; but it must be of real significance. So was developed the drive and fortitude that would carry Percival through his life and the passion that would feed his desire to succeed and plow his own furrow, as Abbott put it.

Percival’s life would unfold in a manner captured by a passage commonly attributed to Ralph Waldo Emerson (though historians find no evidence that he actually said it): Do not go where the path may lead, go instead where there is no path and leave a trail. After overseeing finances of his family’s milling operations and then making a name for himself by studying the culture of the Far East, Lowell improbably entered the field of astronomy. He was inspired by provocative discoveries relating to the planet Mars that seemed to indicate, at least to some observers, the presence of intelligent beings on that planet.

Lowell was thirty-nine years old at the time and threw his considerable energy into pursuing astronomical research, an arena in which he would remain until his death in 1916 at the age of sixty-one. While most American observatories at the time were located near the more populated regions of the country, Lowell realized the need to move away from such areas if he was going to successfully study space. In his 1906 book Mars and Its Canals, he lamented about how civilization, particularly on the East Coast of the United States, was blotting out the sky. Smoke from multiplying factories by rising into the air and forming the nucleus about which cloud collects has joined with electric lighting to help put out the stars, he wrote. Thus, for his observatory he would head to the lightly inhabited Arizona Territory (statehood didn’t come until 1912).

Lowell focused most of his efforts on studying Mars and popularizing the notion of intelligent life on that planet through public speeches, articles in newspapers and magazines and books. But he did expand his research into other areas of the solar system, observing most of the other planets and speculating on their collective origin and evolution. He split his time between astronomical studies at his observatory in Flagstaff; business and family concerns in his hometown of Boston; and miscellaneous travels that often included lecture stops. By all accounts, he was an engaging speaker who usually drew large crowds for his presentations.

Percival Lowell was a dynamic public speaker. Lowell Observatory.

Recognizing Lowell’s skill as a lecturer, the Massachusetts Institute of Technology hired him in 1902 as a nonresident astronomy professor. Toward the end of the year, Lowell presented a series of six lectures highlighting the physical and behavioral characteristics of the Sun and its family of planets, moons, comets and asteroids. He then integrated these observations into an explanation about the formation and large-scale structure of the solar system.

A PLANET OUT THERE AS YET UNSEEN

Publisher Houghton, Mifflin and Company saw value in Lowell’s lectures and in 1903 compiled them into a 134-page book simply titled The Solar System. The content of Lowell’s talks was thus preserved, allowing later students the opportunity to participate in the lectures, as it were. Among other items of interest in this volume are Lowell’s first written thoughts about a possible ninth planet. He cited two lines of supporting evidence, worth sharing here both to understand his reasoning (modern astronomy gives no credence to either of them, but such ideas were common among many astronomers of the time) and to get a feel for the colorful prose that made his presentations and writings popular with the public.

The first regards the relationship between the orbits of meteor streams and planets. Lowell writes:

Another point connected with these meteor streams must be noticed. Each of them is associated with the orbit of some particular planet. The planet in some sense shares with the Sun a control over the stream. It cannot cause the stream to circle round itself, but it can, and does, cause it to pay periodic obeisance to its might. The stream’s perihelion remains at the Sun, but its aphelion becomes its periplaneta. It sweeps about the planet at one end of its path somewhat as it sweeps round the Sun at the other.

The Andromedes are thus dependent on Jupiter, the Leonids on Uranus; while the Perseids and the Lyrids go out to meet the unknown planet which circles at a distance of about forty-five astronomical units from the Sun.

It may seem to you strange to speak thus confidently of what no mortal eye has seen, but the finger off the sing-board of phenomena points so clearly as to justify the definite article. The eye of analysis has already suspected the invisible.

Later in the book, Lowell points out an apparent connection between the orbits of comets and planets:

Jupiter is not the only planet that has a comet-family. All the large planets have the like: Saturn has a family of two, Uranus also of two, Neptune of six; and the spaces between these planets are clear of comet aphelia; the gaps prove the action.

Nor does the action, apparently, stop there. Plotting the aphelia of all the comets that have been observed, we find as we go out from the Sun, clusters of them at first, representing, respectively, Jupiter’s, Saturn’s, Uranus’, and Neptune’s family; but the clusters do not stop with Neptune. Beyond that planet is a gap, and then at 49 and 50 astronomical units we find two more aphelia, and then nothing again till we reach 75 units out.

This can hardly be an accident; and if not chance, it means a planet out there as yet unseen by man, but certain sometime to be detected and added to the others. Thus not only are comets a part of our system now recognized, but they act as finger-posts to planets not yet