2011's eureka moments

A clinical trial that demonstrated beyond doubt the benefit of anti-retroviral drugs in curbing the transmission of the Aids virus, in addition to treating the disease, has been named "the scientific breakthrough of 2011" by the journal Science.

For several years, scientists have suggested that anti-retroviral drugs given to Aids patients may also lower the risk of them transmitting HIV to sexual partners who are free of the virus.

A report on an HIV-transmission trial in Africa in The Independent in 2010, for instance, hinted at such a major side-benefit of anti-retroviral drugs. But it was not until this year that researchers were able to prove it conclusively with a properly controlled clinical trial.

Nearly 1,800 heterosexual couples from nine countries, from Brazil to Thailand, took part in the trial. Pairs of "discordant" couples, where only one partner was infected with HIV, were deliberately selected to take part in the trial to test the idea that anti-retroviral drugs could lower the risk of transmission from one partner to another.

The £50m trial, known by its code HPTN 052, was supposed to have gone on until 2015 before scientists compared couples taking anti-retrovirals to those who were not. But, monitoring this year showed the benefits of the drugs were so clear-cut in terms of preventing HIV transmission that the researchers decided on ethical grounds to give all participants access to anti-retrovirals.

Of the 28 people who became infected with HIV since the trial began, only one belonged to the group in which one of the sex partners was taking anti-retrovirals. This group also experienced some 41 per cent fewer serious health problems associated with HIV compared to the group that was not taking the drugs.

The key discovery was that when anti-retrovirals are taken early enough in the course of HIV infection, long before levels of white blood cells fall to the point that usually leads to the prescribing of the drugs, it can have a dramatic impact on heterosexual transmission – reducing it by some 96 per cent.

Myron Cohen, of the University of North Carolina at Chapel Hill, who led the study published in the New England Journal of Medicine said the strength of the findings surprised him.

At the end of each year, Science lists 10 scientific breakthroughs that its board of experts believes could be considered among the greatest achievements of the past 12 months. The one with the highest number of votes earns the status of Breakthrough of the Year.

Giant leaps: Science breakthroughS of the year

The Hayabusa mission After some near-disastrous technical difficulties and a stunningly successful recovery, Japan's Hayabusa spacecraft returned to Earth with dust from the surface of a large, S-type asteroid – the first direct sampling of a planetary body in 35 years.

Unravelling human origins Studies of the genetic code of both ancient and modern humans revealed that many humans still carry variations in their DNA that were inherited from archaic humans who lived tens of thousands of years ago, such as the mysterious Denisovans in Asia and still-unidentified ancestors in Africa.

Capturing sunlight In vivid detail, researchers in Japan have mapped the structure of the photosynthetic protein used by plants to split water into hydrogen and oxygen atoms. The finding may lead to a powerful source of clean energy.

Pristine space gas Astronomers using the Keck telescope in Hawaii to probe the faraway universe wound up discovering two clouds of hydrogen gas that seem to have maintained their original chemistry for two billion years after the big bang. The discoveries show that pockets of matter persisted unscathed amid eons of cosmic violence.

Microbes in the gut Research into the countless microbes that dwell in the human gut demonstrated that everyone has a dominant bacterium living in their digestive tract. The findings helped to clarify the interplay between diet and microbes in nutrition and disease.

Malaria vaccine breakthrough Early results of a pioneering clinical trial of a malaria vaccine, known as RTS,S, involving more than 15,000 children from seven African countries showed that discovering a malaria vaccine remains possible.

Alien solar systems Astronomers had their first good views of several distant planetary systems and discovered that things are pretty weird out there, including a star system with planets orbiting in ways that today's models cannot explain, a planet caught in a rare "retrograde" orbit, a planet circling a binary star system and 10 planets that seem to be freely floating in space. They are all unlike anything found in our own solar system.

Designer zeolites This year, chemists designed a range of new zeolites, porous minerals used as catalysts and molecular sieves, that are cheaper, thinner and better equipped to process larger organic molecules.

The elixir of youth? Clearing senescent cells, or those that have stopped dividing, from the bodies of mice can delay the onset of age-related symptoms, such as cataracts and muscle weakness. Mice whose bodies were cleared of these loitering cells did not live longer than their untreated cage-mates – but did seem to live better.