ASTRONOMERS announced last month that, contrary to previous assumptions, the orbiting body Eris might be smaller than Pluto after all. Since it was the discovery in 2005 of Eris, an object seemingly larger than what had been considered our smallest planet, that precipitated the downgrading of Pluto from full planet to “dwarf,” some think it may be time to revisit Pluto’s status.
Most of us can’t help rooting for Pluto. We liked the idea of a ninth planet, hanging out there like a period at the end of the gorgeous sentence of the solar system. It gave us a sense of completeness. And besides, we were used to it. Pluto’s demotion caused such an outcry because it altered something we thought we knew to be true about our world.
Of course, science doesn’t, and shouldn’t, care what we learned in first grade. If Pluto’s odyssey teaches us anything, it’s that whenever we think we’ve discovered a measure of certainty about the universe, it’s often fleeting, and more often pure dumb luck. The 1930 discovery of Pluto — by Clyde Tombaugh, who coincidentally was born 105 years ago today — is a prime example, a testament not only to Tombaugh’s remarkable perseverance, but also to how a stupendously unlikely run of circumstances can lead to scientific glory.
The search for a ninth planet was led by the Harvard-trained Percival Lowell, a Boston Brahmin who was widely known for announcing the existence of a Martian civilization. Lowell’s hypotheses about a “Planet X” were based on optimistic interpretations of inconclusive data. Many had observed that the orbit of Uranus seemed to be perturbed by a gravitational influence beyond the orbit of Neptune. If the source of that pull could be determined, he speculated, a fellow could point a telescope at that source and find an undiscovered world.
So Lowell, in the Arizona observatory he had built, set out to do just that. His method was not without precedent. But in 1916, after more than a decade of exquisitely delicate mathematics and erratic searching, Lowell died, his reputation as a gifted crackpot confirmed.
Thirteen years later, Clyde Tombaugh was hired by V. M. Slipher, the director of the Lowell Observatory, to resume the search.
At 22, Tombaugh had been making his own telescopes for years in a root cellar on his father’s Kansas farm (where the air was cool and still enough to allow for the correction of microscopic flaws in the mirrors he polished by hand). The resulting telescopes were of such high quality that Tombaugh could draw the bands of weather on Jupiter, 400 million miles away. Ambitious but too poor to afford college, Tombaugh had written at random to Slipher, seeking career advice. Slipher took a look at the drawings that Tombaugh had included, and invited him to Arizona.
For months, Tombaugh used a device called a blink comparator to pore over scores of photographic plates, hunting for one moving pinprick amid millions of stars. When he finally found the moving speck in February 1930, it was very nearly where Lowell’s mathematics had predicted it would be. Headlines proclaimed Lowell’s predictions confirmed.
But there was something strange about the object. It soon became apparent that it was much too small to have exerted any effect on Uranus’s orbit. Astronomers then assumed it had to be a moon, with a larger planet nearby. But despite more searching, no larger object came to light.
They eventually had to face the fact that the discovery of a new object so near Lowell’s predicted location was nothing more than a confounding coincidence. Tombaugh’s object, soon christened Pluto, wasn’t Planet X. Instead of an example of good old American vision and know-how, the discovery was the incredibly fluky result of a baseless dream.
Decades later, this was proved doubly true. Data from the 1989 Voyager 2 flyby showed that the mass of Neptune had been inaccurately measured by about 0.5 percent all along, and that, in fact, the orbit of Uranus had never been inexplicably disturbed to begin with. Percival Lowell had been hunting a ghost. And Clyde Tombaugh, against all odds, had found one.
All of which is to say, science is imperfect. It is a human enterprise, subject to passions and whims, accidents and luck. Astronomers have since discovered dozens of other objects in our solar system approaching Pluto’s size, amounting to a whole separate class of orbiting bodies. And just this week, researchers announced that they had identified 1,235 possible planets in other star systems.
We can mourn the demotion of our favorite planet. But the best way to honor Lowell and Tombaugh is to celebrate the fact that Pluto — while never quite the world it was predicted to be — is part of a universe more complex, varied and surprising than even its discoverers could have imagined.
Of course, for those of us who grew up chanting “My Very Eager Mother Just Served Us New Pizza,” nine planets will always seem more fitting than eight. New facts are unsettling. But with the right mindset, the new glories can more than make up for the loss of the old.
