Inevitably, year-end lists invite plenty of debate and criticism, and Scientific American's is no exception. Certainly, we could have included the discovery of new worlds beyond our solar system, including Kepler 22 b, an exoplanet in the "Goldilocks" zone of habitability, as well as the first known Earth-size exoplanets. Or noted the accumulating evidence suggesting that hydraulic fracturing, or fracking, to retrieve natural gas is likely to contaminate water supplies. (Final New York State regulations, expected in mid-2012, could determine the future of fracking in the U.S.)

Other candidates included the report of a new target against HIV, in which a doorway to infection (the so-called CCR5 receptor on immune cells) is blocked; the demonstration (using diamonds) that quantum entanglement can occur in everyday objects; and the MESSENGER spacecraft's photos of the planet Mercury, the first ever taken from orbit.

Some of our top choices could very well have an immediate effect on our lives. The impact of others may not be felt for years. Some discoveries may vanish altogether. We'll just have to see how things turn out in the years ahead. But no matter what, 2011 held big surprises in science and technology.

IBM's Watson Computer Wins on Jeopardy!

In February IBM's Watson capitalized on its advanced natural language–processing, information retrieval and machine-learning capabilities to soundly defeat two highly accomplished Jeopardy! champions—Ken Jennings and Brad Rutter—at their own game.

Although some pundits have dismissed the event as a stunt, Watson's abilities should prove useful outside of game shows. In 2012 look for Watson to begin applying its advanced analytics skills in the health care industry to improve patient diagnosis and treatment. Health insurance provider WellPoint, Inc., is working with IBM to develop software for Watson that will let physicians coordinate medical data based on specific patient needs as well as help identify the most likely diagnosis and treatment options in complex cases.

As far as conversing with computers, most people will be able to relate to the Siri voice-activated navigator on Apple's iPhone 4S this year before they get a chance to interact with anything as sophisticated as Watson. At least the conversation has begun.—Larry Greenemeier

Image of the Watson computer courtesy of IBM

The Sun Sets on Solyndra

In 2010 President Barack Obama hailed Solyndra for "demonstrating that the promise of clean energy isn't just an article of faith." In 2011 the company, which pioneered cylindrical thin-film solar cells, filed for bankruptcy—signaling the end of a long solar boom in the U.S.

For some observers, Solyndra became a symbol of the failures of spending taxpayer dollars to support particular industries (although that role could just as easily have gone to fellow 2011 bankruptcies flywheel-makers Beacon Power or biofuel-maker Range Fuels).

But the truth is, Solyndra failed because solar power is now cheap—conventional silicon photovoltaic modules can be had for roughly $1 per watt, compared with more than $3 per watt for Solyndra's thin-film cylindrical versions. That's a good thing for those who would like to see the renewable technology on more rooftops. In fact, 2011 was a banner year for the U.S. solar industry in terms of installations and the like.

Still, solar power cannot compete on cost with electricity generated from burning fossil fuels in many places—and with the end of government subsidy programs in most parts of the globe following Solyndra's bankruptcy, next year looks set to be even more challenging for solar companies.—David Biello

Image of cylindrical thin-film solar cells courtesy of Solyndra

Gene Therapy Makes a Comeback

Maligned for many years after a 1999 study led to the death of an 18-year-old patient, gene therapy may have finally recovered its promise as breakthrough medicine. In recent years the field has taken positive steps, culminating most recently in the successful—and safe—treatment of hemophilia B.

The new treatment uses a modified cold virus, outfitted with a gene that hemophiliacs are missing. The gene in question allows the body to produce Factor IX, which helps the blood to clot.

The study, published online in December by The New England Journal of Medicine, only enrolled six patients—but after the therapy, four of them could halt their regular Factor IX infusions, and the other two could safely reduce the frequency of their infusions.

Coupled with another success earlier this year (treating children born with severe combined immune deficiency), along with new ways of delivering missing genes, the field is offering renewed hope for treating genetic disorders.—Katherine Harmon

Image of gene therapy courtesy of the Genetics Home Reference a service of the U.S. National Library of Medicine®

7. The Death of Steve Jobs

In many of Steve Jobs's obituaries, the word "genius" seemed to follow within 20 letters of his name. Although some of the coverage bordered on hagiography, the accounts also provided an opportunity for an extended meditation on the nature of technological innovation. In an age of open systems, Apple under Jobs had put in place a culture that tried to strive for unyielding control over the location and positioning of every screw and solder joint in its products.

Jobs's death came at a new peak of success for the company. After many earlier ups and downs, the company had brought to market during the 2000s an array of stunning new offerings: sleek desktop and notebook computers; the iPod, iTunes, the iPhone, the iPad and glass retail stores that seem to serve as magnets for technophiles of every age.

Jobs was infamous for his overbearing management style and sometimes poor treatment of employees. But Apple's achievements may not have resulted from such controlling behavior: James Surowiecki of The New Yorker[commented that this unparalleled success came as Jobs decided to ease up slightly on the compulsiveness button. In an earlier incarnation, Jobs would have never allowed "apps" written by outsiders to run on his machines. Yet the ubiquity of the app has also helped Apple flourish, creating as Surowiecki put it, "market ecosystems" that brought the company to new levels of power and profits.—Gary Stix

See our In-Depth Report, "Steve Jobs: A Technology Visionary Leaves a Huge Legacy"

Image: Courtesy of Spaceageboy/Flickr

The End of the Space Shuttle Program

Oh the places we went!

In a Space Age finale, the launch of Atlantis on July 8 concluded the U.S. space shuttle program. After 135 missions flown in five orbiters over three decades—during which there were the catastrophic losses of two shuttles and 14 astronauts—the routine flight of STS 135 to the International Space Station (ISS) culminated 50 years of almost continuous U.S. manned spaceflight. It also the marked the first time the U.S. gave up its technology to lob humans into space without a clear plan for where it will go after it regains its spacefaring capability.

Now, with Russia's Soyuz affording the only access to the ISS, the U.S. is developing its next generation of space hardware, aiming to send astronauts to destinations beyond low Earth orbit before 2030—most likely the moon or an asteroid.—Michael Battaglia

See our In-Depth Report, "The End of the Space Shuttle Program" as well as all 135 missions in an eight-minute video tribute

Image: NASA

A Hint of Higgs

Has the cagey Higgs boson finally been cornered? In a highly anticipated announcement, two international teams of physicists said in December that the Large Hadron Collider (LHC) had seen blips in its data consistent with the existence of the Higgs, a particle that has long been suspected to exist but has never been seen.

The boson is a natural outcrop of the Higgs mechanism, the leading hypothesis for why the elementary particles that make up atoms, people and planets have mass. The latest data are suggestive but not conclusive; the LHC should settle the matter in 2012. —John Matson

Image showing a signature of a decaying Higgs particle courtesy of CERN

Record-Setting Extreme Weather

Overflowing rivers swollen by persistent rains. Over a million acres scorched by wildfires. Mighty blizzards blanketing the Northeast. One hundred ninety-nine tornadoes in a single day. The weather outside was not just frightful, but also costly. Although the number of extreme weather events have been increasing all over the world in the past few years, in 2011 the U.S. set a record in weather-related damage with 12 catastrophes that cost at least $1 billion each. The damage from the May 22 tornado that devastated Joplin, Mo., alone could top $3 billion.

Extreme weather events have hit other nations hard as well, including Pakistan, the Philippines and Australia, which have all seen heavy flooding. All the events have convinced many experts that with climate change, the weather will, unfortunately, only get worse.—Rose Eveleth

See our In-Depth Report, "Extreme Weather and Climate Change"

Image of Hurricane Irene: NOAA

Faster-Than-Light Neutrinos?

In September a team of researchers unveiled a finding that, if correct, would completely upend physics. In an experiment called OPERA, the physicists clocked lightweight particles called neutrinos making the subterranean journey from Switzerland to Italy 60 nanoseconds faster than they would have moving at the speed of light, which since the time of Einstein's theory of special relativity has been considered the cosmic speed limit.

But most physicists are banking on Einstein; the consensus view is that OPERA's neutrinos only appear to be outpacing light-speed, perhaps because of some unaccounted-for experimental calibration.—John Matson

Image of OPERA's Dario Autiero presenting his group's neutrino result courtesy of CERN

Technology Fuels the Arab Spring

In the last year new technologies didn't just make our lives easier—they completely changed the political structure of the Middle East. Twitter had a hand in bringing down a several dictatorships this year as protestors in the Middle East communicated and organized with one another via social media.

The Arab Spring began in December 2010 after the self-immolation of fruit vendor Mohamed Bouazizi, who was protesting high unemployment rates in Tunisia.  News and images of his protest began moving quickly. Protests in Tunisia ousted President Zine El Abidine Ben Ali in January 2011, and by February resistance brought down the 30-year regime of Egyptian president Hosni Mubarak, forcing him to resign. In August, after months of protests that erupted into a civil war, Libya's dictator since 1969, Muammar Gaddafi, was hunted down by opposition forces and killed.

To see if Twitter played a role in regime change, researchers from the University of Washington in Seattle analyzed millions of tweets, looking for words like "revolution," "liberty," and "Ben Ali." The occurrence of those words spiked as the revolutions got underway. They also saw that the activity from Egypt on Twitter in the days before Mubarak resigned increased 100-fold. The study concludes that the service played a key role in toppling dictators in Egypt and Tunisia, although other experts debate just how much social media tools drove the revolutions.—Rose Eveleth

Image of Tahir Square in Cairo, February 2, 2011, courtesy of Al Jazeera/Flickr

The Japan Tsunami and Nuclear Crisis

On March 11, a catastrophic earthquake and subsequent tsunami killed nearly 16,000 people in Japan—and destroyed a nuclear power complex. In the days and weeks that followed, the Fukushima Daiichi facility went on to experience three meltdowns and, because of a buildup of hydrogen gas, multiple explosions.

After months of heroic efforts workers have officially succeeded in achieving "cold shutdown"—that is, keeping the temperatures in the damaged reactors below 100 degrees Celsius so that the water used to cool the reactors does not just quickly boil away. Such a shutdown state makes it simpler to keep the melted nuclear fuel from undergoing further fission. Unfortunately, leaks in the reactor containment vessels means that water must continue to be added to keep the reactors chilled.

Regardless, much damage has been done. Roughly 88,000 people have been evacuated from an area of 20 kilometers surrounding the power plant, many never to return. Most recently, the utility that owns the plant spilled 45,000 liters of radioactive cooling water, and radioactive elements spewed by the power plant have been found over an area of some 30,000 square kilometers. The multiple meltdowns slowed the pace of new nuclear power plant construction globally—potentially setting back efforts to combat climate change—as well as created the world's newest nuclear park, otherwise known as an "exclusion zone."—David Biello

See our In-Depth Report, "The Japan Earthquake, Tsunami and Nuclear Crisis"

Image of the damaged Fukushima Daiichi nuclear plant courtesy of www.digitalglobe.com