Finding out about our galaxy has been a powerful human desire since time immemorial. Yet we still have much more to learn about just our own planetary system and Sun. Pluto, for example, is between 2.66 and 4.67 billion miles distant from us, depending on its orbital position. And even today, we are still unraveling this celestial body’s secrets.
It was an American, Percival Lowell, born in 1855, who first posited the existence of a planet beyond Uranus and Neptune. A wealthy businessman with a burning interest in astronomy, he spent the last years of his life, from 1906 until his death in 1916, searching for concrete evidence that what he called Planet X existed.
Lowell had both the time and the money to pursue his passion. In 1894 he’d built the Lowell Observatory in Flagstaff, Arizona. This was to be a huge help in his search for Planet X. His belief was that unexplained anomalies in the positions of Uranus and Neptune must mean that an unknown planet’s gravitational pull was displacing them.
Sadly, Lowell was to die at the age of 61 before he could conclusively identify Planet X. In fact, in 1915, his observatory had captured two indistinct images of what would later be called Pluto. But at the time nobody recognized them for what they were.
After Lowell’s death, there was an unfortunate pause in the search for this Planet X. This was caused by a legal dispute between Lowell’s widow, Constance, and the observatory’s management. Happily, the search recommenced in 1929 under the guidance of the observatory’s director, Vesto Slipher.
Slipher entrusted the search for Planet X to Clyde Tombaugh, who was just 23 years of age. Slipher had offered Tombaugh a job after he’d sent some illustrations of Jupiter and Mars to the observatory. As it turned out, it was to be an inspired appointment.
Tombaugh’s search involved photographing the night sky through a powerful telescope. He then had to minutely examine pairs of photographs using a piece of equipment called a blink comparator. The aim was to detect whether any of the bodies in the images had moved. He was to be absorbed in this repetitive task for almost a year before a breakthrough came.
Tombaugh’s moment of triumph came on February 18, 1830, as he studied photographic plates that had been exposed in January. More photographs were taken to confirm the findings and the discovery of this yet-to-be-named planet was announced to the world on March 13, 1930.
The discovery was reported around the globe and was an overnight sensation. Obviously, this new heavenly body couldn’t just be called plain old Planet X. It needed a much more romantic name. In fact, suggestions about what to call the new planet flooded in from all around the world. Constance Lowell had a few ideas but, in the end, it wasn’t her that christened it. In fact, the winning submission was to come from across the Atlantic.
It was a Friday morning in March 1930. At his home in Oxford, England, Falconer Madan read aloud a piece in The Times about the new ninth planet. Listening attentively was his 11-year-old granddaughter, Venetia Burney. She thought the planet should be called Pluto. In Greek mythology, Pluto is the keeper of the underworld. Disney’s famous dog came after the planet, as Venetia was keen to point out in later life.
Madan told his friend Herbert Hall Turner, an Oxford University astronomy professor, about the proposed name. Turner telegrammed the suggestion to the Lowell Observatory, and promptly forgot all about it. Then, on May 1, it was announced that the new planet’s name was to be just as Venetia had suggested – Pluto. Venetia’s reward was a five-pound note from her grandfather, a huge amount of money for a child in the 1930s.
And so the planet Pluto, the furthest in our solar system from the Sun, had now been discovered and named, and that was how things remained for the next few decades. But then, from 1992, doubts about Pluto’s status as a planet began to emerge.
The crux of the matter, as far as top astronomers were concerned, was that Pluto could be seen as just a part of a wider distribution of solid objects in the area of space it occupied. This grouping of objects is called the Kuiper Belt, and the bodies that make up the Belt are not regarded as planets. Now, some solar system graphics in books and museums have appeared without Pluto.
So, given the age of the solar system we live in, it had taken us 4.6 billion years to find Pluto. And then after less than 100 years, we’d lost it again. Of course we hadn’t really mislaid it, and it’s there in the Kuiper Belt as real as any other celestial body. In fact, its status as a planet was to have a partial reprieve.
Along with other bodies in the Kuiper Belt, such as Ceres and Eris, Pluto is now generally regarded by experts as a dwarf planet. This seems a fair compromise since Pluto is in fact only half the width of the continental U.States.
Excitement about Pluto increased in 2006 because of a NASA mission to explore this distant planet, which takes 248 of our years to circle the Sun. The mission would also allow scientists to take a closer look at Pluto’s five moons, in particular the largest one, Charon.
The New Horizons mission, the first to the Kuiper Belt and Pluto, launched in January 2006, reaching Pluto in summer 2015. Among the many things that scientists were keen to study was one particular mystery. The mission had shown extraordinary formations on the surface of Pluto. These structures towered hundreds of feet into Pluto’s atmosphere and were described by NASA as “resembling giant knife blades of ice.”
NASA scientist Jeffrey Moore and his team came up with an explanation. “When we realized that bladed terrain consists of tall deposits of methane ice, we asked ourselves why it forms all of these ridges, as opposed to just being big blobs of ice on the ground. It turns out that Pluto undergoes climate variation and sometimes, when Pluto is a little warmer, the methane ice begins to basically ‘evaporate’ away,” Moore said.
In fact, we can actually observe a similar phenomenon on our own planet, albeit on a much smaller scale. On Earth, the structures are called penitentes and they’re to be found on snow fields at high altitudes. One place you’ll find these weird formations is on Chile’s Chajnantor plain.
NASA’s New Horizons mission continues on its groundbreaking journey of discovery. Its next target is another body in the Kuiper Belt, MU69. Scientists hope to fly the spacecraft within 2,175 miles of MU69, close enough to capture topographic details as small as 600 feet wide. We can expect yet more astonishing pictures from outer space.