The Search for Planet X
Percival Lowell was born on March 13, 1855 in Boston, Massachusetts to the wealthy industrialist Augustus Lowell and his wife Katharine Bigelow Lowell. The family consisted of accomplished academics, businessmen, politicians, and philanthropists that served as role models for Lowell and his siblings. He was an exceptional student of Mathematics at Harvard College, and while he had been interested in astronomy as a young boy, his commitment to the field did not emerge until later in life following his travels to Asia. After spending time in Japan where he wrote several books on the culture of the East, Lowell became interested in Mars, especially in discussions about the possibility of life on the red planet. He was particularly fascinated by markings on Mars that he believed were water canals built by intelligent life. In 1894, Lowell founded the Lowell Observatory in Flagstaff, Arizona to devote more time to his astronomical research on Mars. The location was chosen not only because land was plentiful in the territory, but also because the air quality was free of heavy pollution and ideal for star-gazing. He conducted research at the observatory and published several books about Mars in the following years.
While he spent the majority of his time and focus on the study of Mars, Lowell also conducted research on the other planets of the solar system. The photo to the left shows him observing Venus through a twenty-four inch Clark Telescope at Lowell Observatory. In 1902, Lowell gave a series of lectures at the Massachusetts Institute of Technology about the solar system, and it was in these presentations where he first proposed the idea of a possible ninth planet. By studying the behavior of comets, Lowell observed that they acted like a marker for planets and that just beyond Neptune, a seemingly empty space among a group of comets existed. He also researched unexpected movements in Uranus’ orbit that scientists in the 1700s first detected after the discovery of the planet. Lowell then hypothesized that there must be a ninth planet invisible to the naked eye just beyond Neptune that would both account for the empty space and the disturbances in Uranus’ orbit. In 1905, Lowell began the search for this elusive planet with the help of two other astronomers at the observatory, V.M. Slipher and Carl Lampland.
Due to Slipher and Lampland’s commitments to other projects at the observatory, Lowell created the Lawrence Fellowship and brought on two additional hands to help in the search for the new planet. V.M. Slipher’s younger brother Earl “E.C.” Slipher joined the crew along with John Duncan in 1905. That year, Lowell also hired an MIT graduate, Elizabeth Langdon Williams, to perform calculations from his Boston office. Williams moved to Flagstaff in April of 1919 to continue working on computations for the planetary search, as well as other projects at the observatory.
After assembling his team, Lowell turned his focus towards finding the right equipment to locate the new planet. He had commissioned Alvan Clark & Sons from his home state of Massachusetts to build a twenty-four inch Clark telescope in 1896 for his study of Mars, but the search for a trans-Neptunian planet required modifications to provide a wider field of view. In January of 1906, Lowell purchased a five inch lens made by John Brashear for $350. The new lens on the Clark telescope allowed his team to detect extremely faint objects that Lowell predicted would be within the range of his new planet. With the appropriate staff and equipment, Lowell Observatory began the long search for Planet X.
The hunt for the new planet started off much slower than Lowell had envisioned, and by 1908, very little progress had been made. Lowell Observatory were not the only ones searching for a new planetary object either; in November of 1908, William Pickering at Harvard College Observatory announced his search for “Planet O,” which added an element of competition that reinvigorated Lowell’s own work. He shifted focus to the mathematical side of the exploration and worked closer with Elizabeth Williams to solidify the data. Above are some of the computations she calculated for Planet X as well as a letter to Lowell regarding her progress. The increased focus on mathematical calculations meant that telescopic observations were placed on hold until March of 1911 when the new telescope that Lowell purchased had been completed. The new forty-inch reflector telescope, also built by Alvan Clark & Sons, cost $10,800 and took three years to make. It was instrumental to the search for Planet X and was used until the mid-1960s in various projects at the observatory. In 1911, Carl Lampland also recommended that Lowell purchase a blink comparator, which compared two photographic slides side by side to detect any movement that could indicate a planet. The search for Planet X continued slowly, but the new telescope and blink comparator gave Lowell and his team more hope in the discovery.
For several years, Percival Lowell and his team of computers continued their diligent computations to locate the position of the new planet. The letter above and to the right between Lowell and Carl Lampland detail the proposed coordinates, as well as the mathematical calculations used to determine the potential latitude and longitude of Planet X. Astronomers used these coordinates to capture specific areas of the sky on glass plates. The blink comparator was then used to analyze sections of these slides for any movement that might indicate planetary activity. Observations were captured in a book, such as the one below, with the date, coordinates, observer’s name, and any other details that were relevant to the image captured on the plates. The search continued in a rigorous cycle of producing mathematical computations, taking glass slides of Planet X’s potential location, and reporting any observations. To the right are some calculations produced by Lowell and computers at the observatory during this phase of the project. Below is the opening page of the written manuscript for his book titled A Transneptunian Planet where he discusses why he had begun the search and the mathematical approach necessary to locate Planet X.
Percival Lowell remained dedicated to the search for Planet X until his death in 1916. The quest for a trans-Neptunian planet was long and discouraging at times, and it did not quite live up to Lowell's expectations in the end. Progress was slow and the results were not as significant as the team had initially hoped. Despite the little results, he remained convinced that a ninth planet did exist and that it was waiting patiently to be discovered. Modern scholars not only commend his perseverance, but recognize the revolutionary nature of his work. The pursuit for Planet X was the first planetary search to rely heavily on mathematical calculations, rather than mere observation. While he did not live to witness the discovery, his work laid the foundation for future astronomers to continue the hunt.