Science magazine's breakthrough of the year is a landmark clinical trial that showed HIV drugs can be as effective as condoms in preventing transmission of the virus that causes AIDS. Other top achievements of 2011 included a Japanese spacecraft's return to Earth with dust from an asteroid, progress toward a malaria vaccine and discoveries about modern humans' gene links to cavemen.
The annual top 10 list by the American Association for the Advancement of Science, which publishes the journal Science, appear in the magazine's December 23 issue.
The lead story of the year was an international trial, coined HPTN 052, which showed that people taking anti-retroviral drugs reduced the risk of heterosexual transmission to partners by 96 percent.
The breakthrough was described by some experts as a tipping point in the fight against AIDS, 30 years after the epidemic first surfaced.
"People were interested in the idea of treatment as prevention, but it created a hurricane-force wind behind the strategy," said lead investigator Myron Cohen of the University of North Carolina's School of Medicine.
The trial began in 2007, enrolling 1,763 heterosexual couples -- in which one partner was HIV positive -- from Botswana, Brazil, India, Kenya, Malawi, South Africa, Thailand, the United States and Zimbabwe.
"The HPTN 052 results and other recent successes have raised hopes that combining such interventions can now end AIDS epidemics in entire countries, if not the world," the journal said.
-- Japan's Hayabusa spacecraft survived a host of technical failures but returned to Earth, albeit three years late, with a dusting of particles from the Itokawa asteroid. An analysis showed that solar wind discolors asteroids.
-- Following 2010 studies that showed Europeans and Asians inherited two to six percent of their DNA from Neanderthals, new analyses showed that breeding with cavemen gave modern humans an immune boost, and raised new questions about whether the dextrous tool-maker Australopithecus sediba is our direct ancestor.
-- Japanese researchers mapped Photosystem II, a protein that plants use to split water into hydrogen and oxygen atoms, a structure that could lead to powerful advances in clean energy.
-- Astronomers detected pristine clouds of hydrogen gas much like that from the first few hundred million years after the Big Bang. Another team finds a star with almost no metals, like the earliest stars in the universe, suggesting pockets of deep space have survived "unscathed amid eons of cosmic violence.
-- Researchers gained a new understanding of the microbes that dwell in the human gut, with some thriving on high-protein diets while others prefer vegetarian fare.
-- The search for the world's first malaria vaccine RTS,S, received a boost with the release of early results from a major clinical trial showing it cut risk by about half in African children.
-- Strange discoveries in deep space included a cluster of six large planets orbiting a star named Kepler 11 about 2,000 light-years from Earth, a gas giants that orbits in the opposite direction of its parent star, 10 planets that seem to orbit no stars and all, and one planet that is orbiting two stars.
-- Industrial chemists designed a host of new porous minerals, called zeolites, which could save money and offer a new boost to the oil and gas industry, air and water purification processes and household laundry detergents.
-- Getting rid of old cells may help improve life quality, according to scientists who using lab mice discovered that clearing these senescent cells from the body can delay cataracts and muscle weakness.