We lost a planet but solved that nagging puzzle

It was the year when the solar system's second favourite planet was voted out of existence, and when the missing link between fish and land animals was found. It was also the year when the spectre of global warming became ever more alarming but where mathematicians and medics hailed the solution of a century-old puzzle and the world's first cancer vaccine respectively. The SCMP looks at its five top scientific events of the year.

1 Pluto is cast out by the planets club

It was a decision that provoked unexpected outrage and tears from millions of children as their parents broke the news to them that the 'little Pluto' that ends the kindergarten ditty 'let's sing about our nine planets' is officially no longer a planet.

Little Pluto, it turned out, was just too little to last. It was demoted in August by the 2,500-member International Astronomical Union from ninth planet to the humiliating title of pluton or 'dwarf planet' - essentially just another rock drifting out in a void of space called the Kuiper Belt.

This was a story that transcended science. There were protest songs, T-shirts, bumper stickers and a global internet campaign for the reinstatement of the faraway rock discovered only in 1930 but which quickly took a firm hold of the popular imagination and even had a Disney character named after it.

The protests were less about logic than our sense of fair play. Everyone loved Pluto because it was the little outsider, the baby of the solar system, the plucky little survivor clinging on to the edge of our known solar system.

Kicking it out of the planets club might make scientific sense but to most of the world it just seemed like the worst kind of bullying. Don't be surprised to see Pluto make a return.

2 The fish that walked

Its name means 'large, shallow-water fish' - and the discovery of the Tiktaalik may be one of the most important fossil finds ever.

The Tiktaalik is the missing link between fish and land animals, showing how creatures first crawled from the oceans to dry land more than 375 million years ago and providing a vital lost piece of the evolutionary jigsaw.

It was a scary predator with a crocodile-like head that grew up to 2.75 metres long and had a skull, neck and ribs similar to early land animals but a jaw, fins and scales more like a fish.

The fossil of the Tiktaalik was found on Ellesmere Island in Canada, now 960km from the north pole but in the Devonian era when it lived, a subtropical land mass where it wallowed in small streams in between what must have been terrifying sortees out on to dry ground.

3 Proof our Earth is melting

The discovery of 2006 that should worry us all most is that the Antarctic and Greenland ice sheets are melting at an ever faster rate. Scientists also found that by end of the century, Siberia as we know it will cease to exist. All its frozen ground will thaw, releasing 1,000 gigatons of carbon stored in the permafrost and accelerating dramatically the effects of global warming.

It isn't just the thawing that we have to worry about, a study by the University of Alaska in 2006 discovered. The carbon stored in permafrost may emerge as methane, a greenhouse gas 20 times more powerful than carbon dioxide.

Even Lapland was short of snow this Christmas - and scientists have found that if global warming continues at current rates, the Arctic will be largely free of ice in the summer by 2040, raising land temperatures further and spelling catastrophe for first polar bears, then artic wildlife and then potentially the rest of mankind.

4 A vaccine for cancer

In a potentially huge breakthrough for women's health, the world's first anti-cancer vaccine was launched in 2006. Gardasil is reckoned by some experts to reduce incidence of cervical cancer - one of the biggest killers of women - by up to 70 per cent.

The treatment, developed by US pharmaceutical company Merck and Co, involves three injections administered over a six-month period and is aimed at females aged nine to 26. The vaccine protects against two strains of the sexually transmitted infection HPV that can trigger the cancer.

While the treatment is being hailed as the medical advance of the year, the beneficiaries are likely to be those who can afford the treatment, in the short term at least. Gardasil's makers estimate the injections will cost around HK$1,500 a shot in Hong Kong.

5 The solving of the Poincare Conjecture

Most people will have no idea what the Poincare Conjecture is, let alone how to go about solving it. Nevertheless, the cracking of a riddle that has tied mathematicians in knots for more than a century caused enormous excitement among boffins the world over in 1996 and was hailed by the US journal Science as 'breakthrough of the year'. The Poincare Conjecture, set in 1904 by Henri Poincare, was previously one of the big unsolved problems in the realm of mathematics. Put simply, it describes a test for showing that space is equivalent to 'hypersphere' - the three-dimensional surface of a four-dimensional ball.

Sounds simple? Not so. It took 98 years before Russia mathematician Grigori Perelman was able to outline a potential solution on the internet. In 2006, 102 years after the conjecture was set, three separate teams - including US-based mainlanders Zhu Xiping and Cao Huaidong - wrote papers that completed Perelman's solution. A century of head-scratching by eggheads was ended - and a popular weekend pursuit for obsessive mathematicians lost forever.