Searching and exploration missions to discover Pluto
Welcome to my blog" Mystery of Galaxy". 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.
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| Pluto |
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.
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| Ceres Source: Justin Cowart / CC BY |
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 in1804. 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. 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.
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| Asteroid Belt Source: Theresa knott at English Wikibooks / CC BY-SA |
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,
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| Lowell Observatory in Flagstaff, Arizona, Source: Packbj / CC BY-SA |
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 Planet9 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. 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 grand daughter over breakfast. Falconer Madan was one of those gloriously19th 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 grand dad 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 kind 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.
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| Charon Source: User:PhilipTerryGraham / CC0 |
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. 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 setup 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, was also sighted. But it was January 5, 2005 that changed our solar system forever. That was the day Mike Brown discovered Eris.
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| Eris Source: ESO/L. Calçada and Nick Risinger (skysurvey.org) / CC BY |
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 clear edits 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. 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.
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