Over four billion kilometers away from us
lies a distant, frigid world. On its barren surface, nitrogen falls as snow. Vast plains of frozen methane lie in the shadow
of ice water mountains. From the surface of this hostile place, the
sun appears nothing more than a star, a single pinprick of light among millions. The name mankind gave this silent world? Pluto. Discovered in the midst of the Great Depression
by a former Illinois farm boy, Pluto was once the most mysterious planet in our solar system. For decades known only from blurry photographs,
it finally became the focus of a NASA mission in 2006… only for the International Astronomer’s
Union to controversially strip it of its planet status that same year. A dwarf planet that behaves like a comet,
a lifeless chunk of rock that might be home to oceans, Pluto still grips our imaginations. Today we explore the history of this frozen
world… and journey to the very edges of our solar system. The Search for a New World
On January 1, 1801, a Catholic priest looking through his telescope on the island of Sicily
noticed a strange light. It was the dawn of the 19th Century, and the
astronomical world was still reeling from William Herschel’s discovery of Uranus twenty
years earlier. For the entire span of human history, humankind
had lived in a solar system of only six planets. Mercury, Venus, Mars, Jupiter and Saturn had
all been known to astronomers since the days of Babylon. While Galileo and Huygens had documented Jupiter
and Saturn’s moons, there had been nothing to suggest there might be other worlds out
there, lurking in darkness. Then March 13, 1781 had rolled around and
Herschel had casually declared Planet 7 was a Thing now. And now here was Father Giuseppe Piazzi, squinting
through his telescope one cool Mediterranean night and wondering if he might not have just
discovered Planet 8. The discovery of Ceres was a game changer. Located between Mars and Jupiter, it had somehow
been missed for centuries. After Ceres was officially declared a planet
on December 31, 1801, it triggered a wave of discoveries that would shake up our understanding
of the solar system. The wave started with Pallas, discovered the
next year. It crested with Juno, declared a planet in
1804. And it finally came sweeping down when Vesta
was added in 1807. By the time Neptune was spotted in September,
1846, there were already 12 other planets jostling for space in the heavens. If you’re wondering, “wait, what? I’ve never heard of planet Vesta,” you’re
not the only one. Even in 1846, people were starting to be all
like “13 planets? Yeah, that doesn’t sound right.” Pretty soon, they were agreeing with William
Herschel, who’d long ago dismissed the discovery of Ceres as a mere “asteroid”. Of course, Herschel was right. With the exception of Neptune, all the discoveries
after Uranus had been located in a region between Mars and Jupiter we now call the Asteroid
Belt. Y’know, because of all the asteroids. So began the first great culling of the skies. In 1851, Ceres, Pallas, Juno, Vesta, and Astraea
were all reclassified, and the solar system once more reduced to 8 planets. There things may have stayed forever, were
it not for one man. Percival Lawrence Lowell was born in Boston
on March 13, 1855, just after the great planet finding craze of the 19th Century had fizzled. Luckily for science, though, young Lowell
had two unusual characteristics. One, he was extremely rich. And two, he was extremely susceptible to nonsense. Not long after Lowell turned twenty, the astronomer
Giovanni Schiaparelli announced he’d discovered canals on Mars. Actually, Schiaparelli had discovered channels,
which he gave the sensible Italian name canali. But when that got translated into English
as “canals”, Percival Lowell decided they must’ve been dug by Martians. In Lowell’s mind, the canals were dug by
thirsty aliens desperate to get polar meltwater to the interior of their dry planet. All he needed to do was prove it. In 1894, Lowell used his family’s fortune
to found the Lowell Observatory in Flagstaff, Arizona, for the express purpose of finding
Martians. When that went about as well as you’d expect,
Lowell decided to focus his energies on other discoveries. In 1903, he mathematically proved Neptune’s
irregular orbit meant there must be a ninth planet lurking undiscovered on the fringes
of the solar system. Amusingly, the numbers Lowell used assumed
an incorrect mass for Neptune, and the “irregular” orbit didn’t actually exist. Still, a spark had been fired in Lowell’s
imagination. In 1905, he told his team to stop searching
for Martians, that they now had a new goal. They were going to find Planet 9. The Farmer’s Tale
About a year after Percival Lowell halted his crazy search for Martians in favor of
an even crazier search for a missing planet, an event occurred that would ensure Lowell’s
name went down in history. Clyde Tombaugh was born on February 4, 1906,
into circumstances that couldn’t have been more different from Lowell’s. Where Lowell had been born into a stinking
rich family, Clyde Tombaugh was born to a pair of farmers. Where Lowell had grown up among the leafy
streets of Boston, Tombaugh would grow up on the empty plains of Illinois. Yet the two men, separated by distance, age,
and upbringing, shared one important trait. They were both hopeless dreamers. While Lowell was slaving away down in Arizona,
trying to calculate where in the sky Planet 9 might be, Tombaugh was on his family’s
farm, building his own telescopes out of old Buick parts. While the two never met, it’s easy to imagine
they still shared thousands of moments. Moments when the man and the boy, unknown
to one another, sat on opposite sides of the continent, watching the night sky. By the late 1920s, Tombaugh was making sketches
of Jupiter as seen through his homemade telescope. Soon, he was feeling confident enough in his
abilities to send those sketches to astronomers. That included Lowell Observatory. If the discovery of Pluto was a Hollywood
movie, this would be the point where a grizzled old Percival Lowell leafs through Tombaugh’s
sketches and growls, “by God, this boy’s got something!” But Lowell didn’t say anything like, for
the good reason that he’d died nearly a decade ago, in 1916, his search for Planet
9 still unresolved. But Lowell’s death hadn’t meant the end
of Lowell Observatory. The wealthy old eccentric had left his team
a pile of money to continue his work. And when that team saw Tombaugh’s sketches,
they decided, by God, this boy really did have something! In 1928, Tombaugh received a letter asking
him to come to Lowell Observatory to work as a junior astronomer. For the farm boy from Illinois, it was a dream
come true. Albeit with one Pluto-sized caveat. The job waiting for the Tombaugh was about
as glamorous as renewing a driver’s license. Tombaugh was to sit out in the observatory
all night long in the freezing cold, photographing over and over again the section of sky where
Lowell had theorized Planet 9 would be. He then had to compare those photographs for
a tiny pinprick of moving light. Seen from Earth, planets look no different
than stars, they’re all just little glowing dots. The difference is that stars appear stationary
in photographs of the night sky, while a planet appears to move across the frame. It was this tiny movement Tombaugh was looking
for, the telltale sign of Lowell’s missing planet. Boy was it boring. From April, 1929, to February, 1930, Tombaugh
spent night after night sat under the clear Arizona sky, gazing up at the cold blue glow
of a billion stars. It’s hard to imagine what Tombaugh felt
during that long year of false starts, empty hope, and grinding failure. Maybe he wondered what he was doing here,
why he’d left home behind for a life of neck cramps and numb buttocks. Or maybe he simply thought back to his childhood,
spent sat in so many fields staring up at the stars like this, and marveled at how far
he’d come. Clyde Tombaugh couldn’t have known it back
then, but he was about to go even further. Before a year was out, Tombaugh was going
to go from mere Junior Astronomer to Discoverer of Planets. Eldritch Yuggoth
The day February 18, 1930, started at Lowell Observatory like any other. As he had for nearly a year, Clyde Tombaugh
was examining plates of the night sky through a blink comparator, a device that quickly
flicked between photos to make spotting movement easier. By now, the farm boy from Illinois had matured
into an oddly handsome young man of 24. With his small, round spectacles, neat hair
and square jaw, the Tombaugh of 1930 looked not unlike a geekier version of the film star
Harold Lloyd. The plates Tombaugh was comparing that day
had both been taken back in January, but were only now just being looked at. As Tombaugh cycled through the images, he
saw precisely what he’d seen so many times before. Immovable star fields, unchanging dots of
light. The great, familiar universe. With one exception. There, captured on just two plates, was a
tiny blur, a flicker of light that moved across the star field. Out of the blue, Tombaugh had done it. He’d discovered Lowell’s missing planet. Over the next month, astronomers and observatories
across the world replicated Tombaugh’s feat, ensuring it wasn’t just some embarrassing
mistake. When it became clear that there was no mistake,
the astronomy community exploded. Eighty years after Neptune had been discovered,
this one-time farm boy had done it. He’d found the newest planet! The discovery of Planet 9 was announced on
March 13, the anniversary of both Percival Lowell’s birth and the discovery of Uranus. Just one day later, a former Oxford don was
sat in his dining room in England, reading the news aloud to his 11-year old granddaughter
over breakfast. Falconer Madan was one of those gloriously
19th Century academics who could beat you at chess while simultaneously lecturing on
paleontology, playing a game of racket sports, and discussing the works of Lewis Carol. But for our story today, the marvelous thing
about Madan was his 11-year old granddaughter, Venetia. As her granddad read about the discovery of
this new planet, Venetia casually remarked that they should name it Pluto, after the
God of the Roman underworld. Madan was so tickled that he called his old
friend, the astronomer Herbert Hall Turner, to tell him. Turner then immediately called Lowell Observatory
to tell them. Thousands of kilometers away, in Arizona,
the team at Lowell were weighing up the names Minerva and Persephone when the call came
through with Venetia’s suggestion. Tombaugh knew they had their name. But while Venetia had suggested Pluto because
a planet so dark and cold reminded her of the Roman underworld, Tombaugh chose it for
a much more prosaic reason. How do spell “Pluto”? Well, you start with a P and an L… the initials
of Percival Lowell. The discovery of Pluto was like a media bomb
going off. Eager for an uplifting story amid the gloom
of the Great Depression, newspapers pounced on it. Pluto was breathlessly described as being
potentially bigger than Jupiter, or maybe a whole new class of planet. Tombaugh was held up as an all-American hero:
a boy who built his own telescopes and discovered a planet. Up in New England, the great horror writer
H.P. Lovecraft was so intrigued that he incorporated
Pluto into his story The Whisperer in Darkness as the eldritch planet Yuggoth. Pluto made Tombaugh’s career. He was the only American to have ever discovered
a planet. For the rest of his long life, he’d be feted
across the country. Little did he know the day would eventually
come when the world decided Pluto wasn’t a planet after all. The Unknown Planet
After all the excitement of discovering and naming Pluto finally died down, one inconvenient
fact became clear. We knew absolutely nothing about it. Oh sure, we knew that it was smaller than
the gas giants. We could guess that it was extremely cold. We knew, also, that it had a strange, reddish
glow. But exactly how big Pluto might be, or what
that extreme cold meant for its composition, was something we physically had no way of
finding out. All we knew for sure was that it was a dead
world, spinning in the darkness beyond the ice giants, so remote as to be unexplorable. And that’s kinda how things stayed for decades. Pluto was added to school textbooks. It was lovingly built out of papier mache
and attached to dioramas. But no-one knew what it was. In fact, the clearest clue to Pluto’s true
nature came in 1951, when Gerard Kuiper theorized a disc of distant, icy objects lying beyond
Neptune’s orbit. But, for most of the public, the next time
they heard of Pluto again was in the summer of 1978. That’s because 1978 is the year we discovered
Pluto’s moon. Known as Charon, after the ferryman who takes
souls to the Roman underworld, Pluto’s moon was interesting for all sorts of scientific
reasons. But Charon’s discovery overshadowed another
simultaneous discovery: that Pluto might have a faint atmosphere. If it did, it would be a strange atmosphere,
one that turned to vapor and rose up in the Plutonian spring, before turning to nitrogen
snow and falling back to earth in the winter. For University of Texas student Alan Stern,
it was this idea of a seasonal atmosphere that captured his imagination. Alan Stern. Remember that name. He’s gonna be pretty important. The next few years passed with only tantalizing
news about the ninth planet. In 1985, a series of eclipses as Pluto and
Charon slipped in front of one another allowed astronomers to determine that Pluto was only
half as big as initially thought – smaller even than the Moon. But while this was an important discovery,
it paled against the space news coming from elsewhere. The end of the decade saw Voyager 2 fly past
both Uranus and Neptune, beaming back the only close up images we’ve ever seen of
the ice giants. Compared to seeing the cold, opaque skies
of Uranus, and the swirling blue clouds of Neptune, what was the discovery of Pluto’s
size? It didn’t help that there was no way to
get the Voyager probes to Pluto. As they whizzed towards the edges of the solar
system, it seemed mankind would never get a good look at our most-distant neighbor. The fact we did is due to a postage stamp. Well, it’s due to 8 postage stamps to be
exact, a whole series the US Postal Service issued in 1991, celebrating space exploration
with images of each planet taken by probes. But, for Pluto’s stamp, there was merely
a greenish dot and the words NOT YET EXPLORED. When Robert Staehle saw those words, he felt
the sort of blind anger most of us only feel towards parking wardens. A scientist at NASA’s Jet Propulsion Laboratory,
Staehle knew Pluto was currently at its perihelion, the point when it’s closest to the sun. He also knew that there was a window coming
up, between 2001 and 2006, when any Pluto probe could slingshot itself off Jupiter’s
gravity and shave three years off a potential mission. When he saw that stamp, Staehle decided he
would be the one to change those words to FINALLY EXPLORED. But for all his grand dreams, Staehle ultimately
would not be the man who revealed Pluto to the world. Instead, that job would fall to Alan Stern. Riding the Pluto Express
As Staehle began drumming up interest at the JPL for a mission to Pluto, discoveries were
being made elsewhere that would seal Pluto’s fate. In 1992, the Mauna Kea Observatory announced
the discovery of 1992QB1, a lump of rock beyond Neptune popularly known as Smiley. This was the first object from the Kuiper
Belt ever seen by humans. And it raised a worrying question. If there were other objects out there near
Pluto, did that mean Pluto wasn’t unique? For now, though, those questions could wait. At the JPL, Staehle and his team were hard
at work on something they called the Pluto Kuiper Express. As they worked, the years passed. In January, 1997, Clyde Tombaugh died at the
age of 90. One of his last wishes was a half-joking request
to be buried on Pluto. Finally, in 2000, Staehle and his team took
the Pluto Express to NASA science chief Ed Weiler, fully expecting to get the go-ahead. Weiler took one look at their proposal…
…and threw them out on their asses. The Pluto Express was projected to cost over
a billion dollars. Over a billion dollars! To visit the runt of the planetary family. Weiler was very firm. No. Goddamn. Way. For astronomers, this was a little like spending
a whole year planning to go to Burning Man, building costumes and buying equipment, only
to be told at the last second they couldn’t afford the bus ticket to Nevada. The fact they eventually got there is thanks
to Alan Stern. We last saw Stern as a college student back
in 1978, getting all excited by the idea of Pluto’s atmosphere. By 2000, he was an adult working at The Johns
Hopkins University Applied Physics Laboratory, commonly known as the APL, and the JPL’s
biggest rival. When Stern’s boss heard the JPL’s Pluto
Express plan had crashed, he remembered Stern’s fascination with Pluto. Why don’t you write your own proposal? He asked. So Stern did. On September 18, 2001, Stern and his team
delivered NASA a proposal, showing the APL could do a Pluto visit for half the cost of
the JPL’s dead project. Faced with such frugal figures, NASA relented. They passed a funding request onto the White
House… …which promptly shot it down in flames. This was the immediate post-9/11 era. The War on Terror was just gearing up. Who the heck had money for Pluto? When Stern got the news, he knew he had to
act fast. The next year, 2002, was the date of the decadal
survey of scientists. A canvassing of scientific opinion across
America, the survey is used once a decade to select which science projects to fund. And Stern was determined that Pluto should
be project number one. Through the next few months, Stern campaigned
hard for Pluto. He emphasized the one-shot nature of the Jupiter
window. Hammered into skulls how much more expensive
it would be in ten years’ time. Pointed out over and over how Pluto was the
one planet we didn’t know a damn thing about. Finally, in July, 2002, the results of the
decadal survey were published. There, at the very top of projects scientists
considered necessary to fund, sat visiting Pluto. The White House released the funds shortly
after. For Alan Stern and the APL, it was the moment
they’d been dreaming of. Finally, nearly 15 years since Voyager 2 visited
Neptune, the chance to explore Planet 9 was here! Sadly, Planet 9 was not going to remain a
planet much longer. The Man Who Killed Pluto
Back in 2000, 7-year old Will Galmot had been visiting an exhibition on the planets at the
Hayden Planetarium in New York, when he noticed something odd. Whoever arranged the exhibition had only set
up models of 8 planets. There was no Pluto. The name of the guy who had set up that exhibition? Neil deGrasse Tyson. Ever since the 1992 discovery of Smiley – remember,
that other object out near Neptune? – parts of the scientific community had
started to wonder if Pluto was really a planet. Their most vocal member was Neil deGrasse
Tyson, but he wasn’t the only one. At the Palomar Observatory in California,
astronomer Mike Brown was searching for evidence that Pluto wasn’t unique. In the dying days of 2004, he found it. Haumea is an object in the Kuiper Belt, a
lump of rock spinning so fast it resembles an elongated egg. Importantly, it’s almost the same size as
Pluto. Barely three months after Haumea was discovered,
another object similar to Pluto, Makemake, was also sighted. But it was January 5, 2005 that changed our
solar system forever. That was the day Mike Brown discovered Eris. Orbiting between 10 and 14 billion km from
the Sun, Eris is one of the most distant objects in our solar system. More importantly, though, it’s not just
almost the same size as Pluto, it has a bigger mass. If Pluto was a planet, then there was no way
Eris wasn’t a planet, too. The discovery of Eris was like the 19th Century
great planet rush all over again. Realizing we were in danger of winding up
with more planets than we could reasonably expect schoolchildren to remember, the International
Astronomer’s Union set up an emergency committee to define what the heck a planet was. Initially, it looked like the committee was
going to recommend bestowing planet status on Eris, and maybe even turning our old friend
Ceres back into a planet. Sadly, it was not to be. On August 24, 2006, the IAU met in Prague
to vote on what defined a planet. In a last minute session attended by only
ten percent of conference-goers, they voted to classify a planet according to three points:
1. An object that orbits the sun. So, no moons allowed. 2. An object with enough mass to be nearly spherical. Goodbye Haumea, you weird, egg-shaped thing. And, 3. An object with enough mass to have cleared
its own orbital path. It was on point three that Pluto, which crosses
paths with other Kuiper Belt Objects, fell down. Along with Ceres, Eris, Haumea, and Makemake,
Pluto was reclassified as a dwarf planet. So where did all this leave Alan Stern’s
New Horizon’s mission? Already on its way to Pluto. The probe had launched on January 19, 2006,
back when Pluto was still a planet. By the following year, as it swung by Jupiter
to get its gravity assist, it was no longer destined to explore Planet 9, but merely a
particularly big Kuiper Belt Object. In late 2007, New Horizons entered shutdown
mode, keeping itself asleep as it whizzed out of Jupiter’s orbit, headed for the very
edges of our solar system. Back on Earth, Alan Stern was tearing his
hair out, trying to get people to believe that Pluto was still a planet. But while Stern’s efforts to get Pluto reclassified
as a planet would go unheeded, his efforts to get people to care about the frozen world
wouldn’t be ignored. In 8 short years, Pluto was going to become
news again in the biggest possible way. Beyond the Infinite
In the end, New Horizons only spent a few short hours in the company of Pluto. A few short hours in which it snapped pictures
as frantically as possible. In those short hours, it changed our conception
of Pluto forever. Yep, it’s finally time. Time for our story to reach the moment you
all remember. That moment on July 14, 2015, when New Horizons
gave us the first detailed look at Pluto in human history. The photos that flew back to Earth, crossing
four billion empty kilometers of space, showed a world unlike anything we could ever have
imagined. (NOTE TO EDITORS: It might be cool to get
a quick montage here of all the photos, with some suitably epic music, before we go back
to Simon. The photos are all public domain so we can
use as many as we like!) There was the great heart shaped plain that
covered Pluto’s southern hemisphere, like a message welcoming us to the Kuiper Belt. There was the mysterious, dark region, later
named Cthulhu Macula after H.P Lovecraft’s legendary monster. And there was the faint glimpse of an atmosphere
we saw as New Horizons took one last photo, revealing the haze around the dwarf planet. We saw incredible things. Things like the smooth, pattered surface of
Sputnik Planitia, suggesting a heat source somewhere beneath the surface, constantly
renewing the methane ice. Others we only inferred, like the fact that
this internal heat source might mean Pluto has a subsurface ocean, a dark, churning sea
of water that’s billions of years old. Imagine that for a second. Imagine an ocean that has never seen light,
that has never been seen by human eyes, waiting to be explored at the outmost limits of our
solar system. Touchingly, New Horizons did something else,
too. It took with it an ounce of Clyde Tombaugh’s
ashes. Nearly a century on, the astronomer had finally
got to meet his discovery. Today Pluto is still a mere dwarf planet. Nearly a decade of campaigning by Alan Stern
has been unable to get our ninth planet reinstated. But maybe it doesn’t need to be. As technology improves and our telescopes
get ever more powerful, the focus of our explorations is shifting away from our nearest neighbors
and further out, to the very fringes of our solar system. Nowadays, the Kuiper Belt is a magnet for
scientists trying to understand how our cosmic neighborhood came to be. And at the heart of any attempt to understand
this remote region lies Pluto, the greatest Kuiper Belt Object of all. Humanity may have been looking toward Pluto
for over a century, ever since Percival Lowell first theorized its existence. But the story of our relationship with this
frozen world is only just beginning.
