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  • Paul Rutherford

DID THE EARTH MOVE?


"A rose by any other name would smell as sweet". Romeo & Juliet, Act2 Sc 2 For Juliet, the Montague family name is just a label; to her, it doesn't effect what Romeo is. "'Tis but thy name that is my enemy." But for everyone else in Shakespeare's early tragedy, the name Montague (like Capulet) means everything. It defines their loyalties, their loves, their hatreds, their place, and indeed, their world. The names we give things shape our reality. NOT SO EASY METHOD I've been thinking about this a lot since hearing a radio discussion about, of all things, the down-grading of Pluto. (From "star-cross'd lovers" to astronomical classification systems - these blogs aren't just thrown together.) In case you missed the memo, Pluto is no longer a planet. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Perhaps you just know that; perhaps you have have a mnemonic to remember it by: My Very Easy Method Just Speeds Up Naming Planets Not any more it doesn't. An axiomatic truth that has been part of your definition of the world - indeed, the Universe - since you were born, is now wrong. Pluto is a dwarf, and part of the Kuiper Belt. Clear? The process of how this happened is a fascinating case study in how unpacking the meaning of a term can have a profound impact on how we see reality. WHAT IS A PLANET? The word - like many things astronomical - is Greek, from planome, meaning 'I wander'. As the ancients looked into the night sky, they noticed that some things were static (at least in relation to one another) while a few bodies moved about. They were the 'wanders'. Given the limits of view (radio telescopes ere in short supply at the time), seven wanderers / planets were identified; the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. (By the way, these were also the origin of naming the days of the week - but that's another story.) That model held until the 16th Century, when Copernicus posited a heliocentric model, and showed that one of the 'planets' was at the centre of things. A few years later, Galileo's improvements on the telescope provided evidence that this was, indeed, the case. It took another 150 years for Uranus to appear (1781), followed by Neptune in 1846. Watching disturbances in the orbit of the later, by the end of the 19th Century astronomers were 'predicting' the presence of another planet, but it took another thirty years (and a lot of money from wealthy Bostonian Percival Lowell) to actually see Pluto. And so our nine-planet system was complete. Until 2005.

During the 1990s, many new objects were discovered in the outer reaches of the solar system, some of which looked remarkably similar to Pluto (small and icy) and exhibited similar properties (like an odd orbit). Were these new planets or a new category? In 2005, a team at the Palomar Observatory really threw a spanner in the works with the discovery of three new celestial bodies in the 'trans-Neptune' region: two were smaller than Pluto (Haumea and the wonderfully-named Makemake), while Eris was larger. So, is size does matter, then for a short while the solar system certainly had 10 planets, and it could be argued that it had 12. I bet you missed THAT memo. For many astronomers this was starting to get out of hand. The more powerful their technologies, the greater their reach; the greater the reach, more objects they discovered wandering the sky. The planetary system was starting to look rather crowded. Time to challenge the Greek's definition. WHAT IS A PLANET? REDUX The 26th meeting of the International Astronomical Union took place in Prague in 2006. At it, members were allowed to vote on a resolution to define the term 'planet'. It was the first time they'd ever done so. They eventually agreed on the following: - It must be round. Small objects do not have enough gravitation to overcome their structural integrity, which makes most things in space look like rocks or potatoes. But if you're large enough then eventually your own gravity will pull you into shape. - It must be the primary object that orbits round the sun. Of course, this is to exclude the moons in an orbit (Mars has three, Jupiter six, Saturn eleven, Uranus six, Neptune three, Pluto one). So far, so good for Pluto. It's round and is the primary object in its orbit. Then came the third parameter of the definition: - It must have cleared its orbit of surrounding debris. And with that, Pluto was voted out of the club. Pluto is just part of that that reservoir of icy bodies discovered in 1990s. It's one of many, rather than carving its own path. Pluto is an ex-planet. BY ANY OTHER NAME

It has not been a popular decision. In America, the general population is very attached to Pluto: partly because it was the first planet discovered by an American; mainly because in 1930 Walt Disney's 'Pluto' also appeared, which has become part of the country's cultural heritage. The vote generated emotive news coverage: Solar System Shrinks with Pluto's Demotion Pluto Loses Its Status as Planet Pluto's Planetary Identity Crisis It was as if a small icy ball out in space had developed a personality, been deeply wounded by an assault on its self-image, and would soon be photographed going into The Priory for therapy. Of course, all this says a lot more about us than it does about radio telescopes or a non-planet. Although Pluto's status effects very, very few people in their day-to-day activities, changing the model in which it appears is very, very unsettling: "There are planets, right? Going around the Sun. And there are nine of them, right? And there's a little one on the edge that doesn't go round in a circle, but nips inside the path of one of the big ones. My Very Elegant Mother Just Served Us Nine Pizzas. That's the planets, right? That's the Solar System. The Universe. It is what it is. The economy may be going to hell in a handbasket, and Iraq is a mess, and my team are still second from bottom. But the Solar System is the Solar System. "And you've just taken away the Pizzas! Wooaahhh!! Give me back my Pizza!!!" So much of what we hold to be true is purely a creation of mind. We name parts, we categorise, we classify, we compartmentalise, we label. At one level, that's the basis of intelligent analysis of our world and one of the foundations of the scientific method. At another, it's just a shorthand to help us get through our day, make judgements and take decisions. We all need that toolkit to survive. But it is no more than a toolkit; and occasionally it's good to take out the tools and sharpen them. In researching this piece, my model of the Solar System is considerably richer than when I started: I've traded "Pluto's status" for knowledge about the Kuiper Belt, dwarf planets, 173 moons and the Oort cloud. What I thought to be a truism - so true that it didn't need examination - turned out to be nothing more than a construct based on a falsehood. And I am left wondering how many other of the building blocks that make up my world view are, in fact, fabrications - inherited assumptions that need sharpening? What is your next personal Pluto?

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