Pluto will mark a birthday of sorts on March 23, 2178. No one is likely to be there to celebrate it, of course. Even if humanity is a multi-planet species by then, it would be a decided challenge to visit the tiny, distant world, which measures just 1,477 miles in diameter—or little more than half the coast-to-coast distance of the continental U.S.—lies up to 4.67 billion miles from Earth, and features a surface temperature as low as -400°F. Still that date will be one to circle on cosmic calendars. It takes Pluto slightly over 248 Earth years to orbit the sun, which means that on March 23, 2178, one Plutonian year will have elapsed since the dwarf planet was first spotted, on Feb. 18, 1930.
“NINTH PLANET DISCOVERED ON EDGE OF SOLAR SYSTEM; FIRST FOUND IN 84 YEARS,” the New York Times announced in a front-page, all-caps headline in its March 14, 1930 edition, the day after the Lowell Observatory in Flagstaff, Ariz., announced its big find. “In the little cluster of orbs which scampers across the sidereal abyss under the name of the solar system,” the Times went on, “there are, be it known, nine, instead of a mere eight worlds.”
This Feb. 18 marks 95 years since the Lowell Observatory hit paydirt, an achievement made not by one of the observatory’s professional astronomers, but by amateur Clyde Tombaugh, who at the time was just 24 years old. Not long before coming to work at the observatory, Tombaugh had built his own telescope with which he had conducted observations of Mars and Jupiter. He made drawings of the two planets—drawings he sent to the Lowell Observatory, hoping the astronomers there would offer comment and critique. Vesto Slipher, the director of the observatory, did Tombaugh one better, offering the eager stargazer a job. His assignment would be equal parts tedious and transformative: scanning hundreds upon hundreds of images of the skies, looking for the elusive world known at that point only as Planet X. Percival Lowell, the…
