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.