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Lowell Observatory Archives

The Search for Planet X

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Letter from Percival Lowell to Carl Lampland from August 1912 regarding Planet X's possible location.

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Scan of the opening pages of Percival Lowells written manuscript A Transneptunian Planet. 

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. 

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Percival Lowell ca. 1909.

The Search for Planet X