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On Feb. 18, 1930, astronomer Clyde William Tombaugh began his morning by placing the Jan. 23 and Jan. 29 gem plates on his blink comparator, a device used to allow astronomers to switch, or blink, back and forth between two photographs of the same sky at different times or days. As Tombaugh would later write in his book, Out of the Darkness: The Planet Pluto, co-written with Patrick Moore, “This was a most fortunate decision. Had it been otherwise, Pluto might not have been discovered in 1930.”

But that morning, almost 15 years after Percival Lowell’s death, Pluto was discovered in Flagstaff and, since then, almost every major discovery and fact about Pluto has some connection to Lowell Observatory.

In their new book Pluto and Lowell Observatory: A History of Discovery at Flagstaff, Lowell Observatory historian Kevin Schindler and planetary scientist Will Grundy explore Pluto’s deep connection to the Arizona mountain town.

Pluto surface

An image of Pluto's surface taken during the New Horizon's fly-by mission. Courtesy NASA images


The story of Pluto is one that almost didn’t happen—at least not in the way we know it today. Pluto was bound to be discovered, but if not for the outlandish ideas of the enigmatic businessman, author and astronomer Percival Lowell, the discovery of Pluto may not have happened until much later.

Born of an established and elite family whose motto was occasionem cognosce, “know your opportunity,” Lowell’s desire for excellence ran in his blood.

“[Lowell] came from a leading family, but he was so driven to make a mark that some of his theories were ill advised,” says Schindler.

Lowell, percival

Percival Lowell. Courtesy Lowell Observatory

Many of those ill-advised and provocative theories were published in his three books, Mars (1895), Mars and Its Canals (1906) and Mars As the Abode (1908). Among the many ideas Lowell purported, perhaps his most popular and polarizing was that Mars had once sustained an intelligent civilization that had built canals to tap into the planet’s polar ice caps. Lowell’s unconventional ideas about Mars prompted a surge in study and research to prove or, for many, disprove his theories, as well as invited a handful of science-fiction writers such as H.G. Wells to pursue the idea of Martians in their works.

“He really carved a role for Mars in the popular psyche and would have done the same for Pluto had it have been discovered in his lifetime,” says Grundy. “He sort of shaped a generation and probably inspired a bunch of people to get into science.”

Another fantastic idea, though not exclusively his own, was that a ninth planet beyond Neptune, a Planet X, existed. Uranus, after its discovery in 1781, exhibited perturbations in its orbital motion, leading scientists to believe it was the gravitational pull of another planet. This hypothesis led them to the discovery of Neptune in 1846. But Neptune’s gravitational pull alone could not account for the tugging on Uranus. A ninth planet was still out there. Lowell’s interest in this idea grew from mild curiosity to a full-blown pursuit.

In 1905, Lowell began his search for a ninth planet. 


Lowell never did find Planet X, and he died on Nov. 12, 1916, empty from his fruitless pursuits. Disheartened by his death, Lowell Observatory halted its search for Planet X. Though obsessive, Lowell’s determination laid the groundwork for a more organized and integrated search.

Pluto discovery plates

Pluto discovery photos using Feb. 23 and 29 gem plates. Courtesy Lowell Observatory

“Lowell, I think, was looking for this recognition that he didn’t really get in his lifetime, but after the fact, even though a lot of it wasn’t intentional, if he didn’t found his observatory, Pluto wouldn't have been discovered until a lot later,” says Schindler. “And who knows how Mars research and solar system research would have evolved without his nagging.”

After a decade of court battles regarding Lowell’s will, a new team with new instruments and a newfound excitement began the search again for a ninth planet. When Tombaugh spotted that little dot in his telescope on Feb. 18, he could barely contain himself. But his discovery was kept quiet until March 12 when Lowell director V.M. Slipher sent a telegram to the Harvard College Observatory about the finding.

Clyde Tombaugh

Clyde Tombaugh. Courtesy Lowell Observatory

While scientists were focused on determining the planet’s orbit, Tombaugh’s dot needed a name. Of the hundreds of letters and telegrams that flooded the observatory, one by 11-year-old Venetia Burney from Oxford, England, would determine the planet’s fate. Burney suggested the Roman god of the underworld, Pluto.

“It’s amazing to see how Pluto went from an idea to a dot to a world,” says Schindler. “And all that has Flagstaff ties, from the early searches for it to its discovery and beyond.


In a lot of ways, Pluto and Flagstaff grew up together, says Grundy.

Arizona was not even a territory when Lowell first opened his observatory in 1894, and throughout the years, as Flagstaff and northern Arizona have developed and evolved so have the observations of Pluto, with many of those observations tracing back to Lowell Observatory. Pluto’s first features, its largest moon, Charon, and its atmosphere, all were discovered at Lowell, by Lowell scientists or with Lowell equipment.

Grundy was even one of the scientists who worked on the New Horizons fly-by near Pluto in 2015.

“We wanted to capture that Flagstaff angle [with the book]. Not just the science, but because all that’s happened here, there’s a cultural thing also of ownership,” says Grundy. “There’s a lot of pride here.”

Lowell Mausoleum

The Lowell Mausoleum was constructed in 1923. Photo by Gabriel Granillo

From Pluto-themed novelty gifts and food items to artistic appreciations of the ninth planet, as in Watch For Rocks’ punk-rock anthem “Party on Pluto,” Flagstaff’s love for Pluto is palpable. So when the International Astronomical Union “demoted” Pluto’s classification to a dwarf planet in 2006, it was a bitter moment.

To be a planet, according to the IAU’s current definition, a body must orbit the sun, its shape and mass must create a hydrostatic equilibrium (simply put: it must be a ball) and it must have “kicked all the celestial detritus out of its orbit.” Pluto meets the first two criteria but, as an object in the Kuiper Belt, fails the last.

The decision to demote Pluto, Grundy says, was a political one, with the worry that, if you add Pluto to the solar system, we would also have to add other bodies in the Kuiper Belt of equal or greater size to Pluto.

Schindler, Grundy

Kevin Schindler and Will Grundy. Photo by Gabriel Granillo

“The whole exercise of nomenclature is useful if it draws a distinction between things that are scientifically useful to distinguish,” says Grundy. “It really was a sort of a silly thing, in my mind. Most of us in the planetary science community sort of shrugged our shoulders and continued doing what we were doing.”

Schindler adds that “if anything, it drew more attention to Pluto.”

Lowell Observatory saw its visitations increase, with the public curious about what exactly Pluto was. The observatory took advantage of this newfound curiosity, even changing its donation box to a voting box, encouraging people to “vote with your wallet” on Pluto’s classification.

“In hindsight it was like, ‘Why didn’t we do this before,’” laughs Schindler.

For Schindler, the curious case of Pluto’s classification was trivial, but it offered insight into how science works.

“Pluto is a great conversation for how science is done and how it’s not done. You do learn more and you re-evaluate and you do reclassify things. On the other hand, it shows how it doesn’t usually work like voting. That’s just not how science is done, so it’s a fascinating learning tool.”

Pluto, however we classify it, has personality. It’s the little guy, the underdog, getting picked on by the other planets. It’s the outlier, deep in the shadows of our solar system. It is also the only planet, or dwarf planet, to have been discovered in America. So call it what you will, this is our planet, says Schindler.

Pluto heart

Pluto's famous "heart" is known as the Tombaugh Region. Courtesy NASA images

Pluto and Lowell Observatory: A History of Discovery at Flagstaff is available through The History Press. Lowell Observatory will host a grand reopening of its newly restored Pluto Discovery Telescope on Saturday, March 10. For more information, visit

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