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Alex B. Berezow & Ross Pomeroy RealClearScience Top 10 Lists science

You are a walking sack of bacteria. That's not an insult; it's simply a biological fact. Very roughly, our bodies consist of 10 trillion human cells and an astonishing 100 trillion microbes. Determining exactly who they are and what they do is the goal of the Human Microbiome Project, which published the first large microbiome map in June. Researchers took nose, mouth, skin, urogenital and gastrointestinal samples from healthy volunteers and, so far, have documented some 10,000 different species. Intriguingly, though people may be host to different types of bacteria, in general, similar bacterial genes are present, implying that the microbiome plays the same metabolic and physiological role in all healthy people. Eventually, scientists will want to determine how changes in the microbiome result in disease, such as periodontitis, obesity and inflammatory bowel disease.

Technically, they were convicted of not communicating risk properly, but this seems to be a distinction without much of a difference. In October, disregarding common sense and pleas from scientists across the world, an Italian court sentenced six scientists to prison for failing to predict a 2009 earthquake which struck the city of L'Aquila and killed about 300 people. Of course, as any seismologist would confirm, earthquakes are not predictable. The fallout from this miscarriage of justice will likely include scientists becoming increasingly reluctant to offer their advice in public out of fear of prosecution. Indeed, as one of the convicted scientists said, "I still don't understand what I'm accused of." Neither do we.

6. New particle physics data spells trouble for string theory.

String theory was all the rage back in the day. Theoretical physicist Brian Greene wrote a bestselling book about it, called The Elegant Universe, in 1999 and followed it up with The Fabric of the Cosmos in 2004. Michio Kaku, another theoretical physicist and science popularizer, has also written books on the subject. But those were the glory days. Since then, hard times have fallen upon string theory, which posits that elementary particles are actually made up of tiny, vibrating strings. In November, data from the Large Hadron Collider, a particle accelerator which helped find the Higgs Boson, suggested that the theory has failed in a testable prediction. It's not over yet for string theory, but it's also not looking very good.

5. Arctic sea ice hits new record low.

On August 26th, the extent of Arctic sea ice shrank to 1.58 million square miles, eclipsing the previous low set in summer 2007. The melt continued into mid-September, reaching, at its lowest, 1.3 million square miles, before beginning it's cyclical freezing. An increasingly ice-free Arctic may be the most visual evidence we have of climate change. Moreover, the ice acts as a solar reflector, sending light (and thus heat) back into space. As more dark ocean water is laid bare before the sun, more light is absorbed, warming the water further and causing more ice to melt: a positive feedback loop. The lack of Arctic sea ice may have also given rise to the rare high pressure area over Greenland that caused Hurricane Sandy to take a hard left turn, smashing headlong into the East Coast, where it wreaked $65.6 billion in damages and killed 131 Americans. On the bright side, an ice-free Arctic may open up new economic opportunities.

4. ENCODE helps decode the "junk" in our genome.

It was once believed that the human genome consisted almost entirely of "junk." Relatively speaking, there were only a handful of protein-encoding genes, and the rest of the genome appeared to be mostly useless DNA sequences such as dead retroviruses. How times have changed. The human genome is now understood to be far, far more complicated than previously imagined. Published in September, the ENCODE project, which analyzed 147 different human cell lines, classified at least 80% of the human genome as "functional." Though the project's definition of "functional" was a tad suspect, it did show that the human genome is intricately regulated.

3. Mars Rover "Curiosity" explores the Red Planet.

Blazing streaks of fire, yet only tepid fanfare, followed the Mars Science Laboratory spacecraft as it ascended into space on November 26th, 2011. On-board was NASA's newest Mars rover, the $2.5 billion, SUV-sized Curiosity. Similar flames accompanied Curiosity as she tumbled through the Martian atmosphere to the planet's surface in early August, but this time, the whole world was watching. Despite a harrowing, seemingly impossible landing procedure, the rover touched down safe and sound to onlookers' exuberant cheers back on Earth. Since landing, Curiosity has been busy. Already, she's found concrete proof that water once flowed on Mars. The rover has also discovered organic compounds, though NASA scientists haven't precisely pinpointed whether or not they are of Martian origin.

2. SpaceX becomes the first private company to soar into space.

In 2011, after the retirement of NASA's Space Shuttle program, Americans were left wondering, "Who would pick up the torch of American spaceflight?" This year, SpaceX didn't just pick up that torch and run with it; it blasted that torch into outer space. On May 22nd, the private company launched its Dragon capsule from Cape Canaveral. Three days later, the Dragon successfully docked with the International Space Station. Elon Musk, the company's founder, has also shared plans for an 80,000-person Martian colony. How's that for dreaming big?  

1. The Higgs boson is discovered. 

Perhaps prematurely, last year, we listed the Higgs boson as our #1 story of 2011 because it was probably real. There's no wishy-washiness now. CERN's Large Hadron Collider announced the discovery of the Higgs boson on July 4th. This particle, which helps explain why other particles have mass, was the final missing piece of the puzzle for the leading theory of particle physics, known as the Standard Model. This triumph is bittersweet, however, since its discovery implies that there may not be any more particles to find. (But don't fret; physicists still need to explain dark matter, neutrinos, gravity and a few other things.) Incidentally, the discovery of the Higgs boson also spells more bad news for string theory.