Water of life and other scientific highlights of 2004

Scientific proof that water once flowed on Mars has been voted the breakthrough of the year according to journal Science.

Scientific proof that water once flowed on Mars has been voted the breakthrough of the year according to journal Science.

The discovery topped a list of 10 studies that stood out from the many thousands published by scientific journals in 2004 and raises the prospect that scientists will find evidence of primitive life on Mars, dramatically increasing the chances of there being intelligent beings in a distant solar system.

Two robotic rovers launched by the US National Aeronautics and Space Administration (Nasa) showed beyond doubt this year that the surface of Mars was once flooded with running water. Science said: "The Opportunity rover found the salty, rippled sediments of a huge shallow sea; the Spirit rover discovered rock once so drenched that it had rotted. Their finds mark a milestone in humankind's search for life elsewhere in the universe."

Water in its liquid state is almost certainly essential for the evolution of extra-terrestrial life. If it can be shown that life originated and evolved independently on another planet in the same solar system then it would suggest that life elsewhere in the universe was more common than was thought.

Opportunity bounced down on the vast Martian plain of Meridiani Planum on 25 January, 22 days after its identical twin rover, Spirit, landed on the other side of the planet. Both rovers operated perfectly in the first true geological field survey of Mars from its own surface. Each rover was armed with sophisticated cameras, a magnifying glass, a grinding wheel for exposing fresh rock, an analyser for chemical elements and a suite of other instruments for investigating minerals.

"The two rovers confirmed what many scientists have long suspected: billions of years ago, enough water pooled on the surface of Earth's neighbour long enough to allow the possibility of life," Science said.

Ever since Nasa's Viking probes landed on Mars in the 1970s and took the first close-up images of its surface, there have been tantalising hints that the planet was once covered in rivers and seas. But scientists could not be sure whether the channels, valleys and gullies they had seen through telescopes and orbiting probes were really caused by water erosion.

Data sent back by Opportunity and Spirit over the past year has put the matter beyond dispute, Science said. Mars was once a warm and very wet planet, in marked contrast to the arid, cold, sun-bleached place it has now become. "Thanks to the hardy little robots, we know that Mars of several billion years ago was warm enough and wet enough to have a shallow, salty sea. This sea probably came and went, turning into wind-blown salt flats from time to time, but the puddles spanned an area the size of Oklahoma."

Opportunity discovered exposed bedrock at a crater named Eagle which suggests a regular wet-dry cycle, when pools of water flooded the area and then receded and evaporated to leave behind layers of salt some 300m (984ft) deep. The rover also took photographs of marble-sized crystals of iron-containing haematite, which Nasa scientists have nicknamed "blueberries".

Steve Squyres, professor of astronomy at Cornell University and a leading member of the team that analysed the Opportunity data, said the findings indicate how Mars and Earth had gone their separate ways. "We cannot determine whether life was present or even possible in the waters at Meridiani, but it is clear that by the time the sedimentary rocks in Eagle crater were deposited, Mars and Earth had already gone down different environmental paths," he said.

"What we were seeking was rocks that were actually formed in liquid water so that we could read the record in those rocks, not just to say liquid water was on Mars but to learn something about what the environmental conditions were like," he said.

"Would they have been suitable for life and, importantly, do the minerals that were formed have the capability to preserve for long periods of time evidence of former life?

"That's probably the single most important thing we have found: evidence for minerals at Meridiani that are the kinds of things that are very good at preserving evidence of ancient life for very long periods of time," he said.

On the other side of Mars, the Spirit rover found evidence of shallow groundwater that may have transformed hundreds of metres of volcanic ash into soft, iron-rich rock.

Taken with the latest evidence from orbiting probes, such as the European Space Agency's Mars Express, there is now no dispute that Mars once was home to a huge body of liquid water.

Science judged that the runner-up to the discovery of water on Mars was the finding of another species of dwarf human which lived on the remote Indonesian island of Flores as little as 13,000 years ago. The "startling" discovery, announced in the pages of Nature, the chief rival to Science, overturned the accepted view of human evolution which stated that modern humans co-existed only with the Neanderthals.

Homo floresiensis stood barely a metre tall and appeared to have long arms relative to its size. As Science says: "Sometimes big discoveries come in small packages."

BREAKTHROUGH OF THE YEAR: THE RUNNERS-UP

The smallest human

In October, a team of Australian and Indonesian scientists astonished the world by announcing the discovery of a partial skeleton of a female who belonged to a new species of dwarf human. Dubbed the Hobbit, Homo floresiensis - named after the island of Flores where it was found - stood barely a metre tall and became extinct around 13,000 years ago.

Clone wars

A medical research team in South Korea announced in February that they had successfully cloned a human embryo using the technique that created Dolly the cloned sheep. The scientists said they had no intention of producing a baby, which would be a carbon-copy of another human being. Instead, the purpose was to experiment in producing a cloned embryo a few days old from which they could extract stem cells for medical research.

Gas condensates

The weird world of quantum mechanics became even stranger in 2004 with the announcement that scientists had tinkered with ultra-cold gases known as condensates to induce a set of atoms to behave as a single "superatom". Scientists said the work could help explain what happens when materials become superconductors, the point at which they allow electricity to flow through them with virtually no resistance and hence loss of power.

Hidden DNA treasures

It was once thought that more than 95 per cent of the human genome served no function. But in 2004, evidence emerged that this so-called "junk" DNA contains important codes for controlling the rest of the genome. Scientists found it is full of small gene-like strands that appear to play a role in controlling the way proteins are made by the cell. Central to this role is a process of switching genes on and off - a phenomenon called RNA interference, which has generated much interest in the past five years.

A pair of pulsars

Astronomers found the first known binary system of pulsars - spinning neutron stars that whip tight beams of radiation into space. Some scientists described the discovery as a "watershed" event in the 36-year history of neutron-star studies.

Biodiversity declines

A number of groundbreaking studies documented how many species are in serious decline around the world. Amphibians - frogs, toads, newts and salamanders - are suffering most, with some 30 per cent being threatened with extinction. Half of these species may disappear by the end of the century. Plants, birds, butterflies and mammals are all under pressure from a growing human population, habitat loss, pollution and global warming.

Water, water everywhere

It is essential to life, but water still holds a few chemical secrets of its own. In 2004, scientists discovered that the common model in chemistry of how water is structured, which has been the standard for 100 years, might be wrong.

Private medicine

A number of "public-private partnerships" in medical science produced important breakthroughs in 2004, including a prototype vaccine for malaria and potential vaccines and treatments against HIV/Aids. The partnerships involve cooperation between rich countries, charities, the United Nations, academics and drug companies.

Fishing for genes

A new technique for discovering species of micro-organisms was pioneered in 2004. It involves fishing the seas for pieces of DNA that can be sequenced in order to shed light on the identity and lifestyle of the organism that gave rise to it. One team of biologists sailed across the Sargasso Sea, deciphering genomes from the life forms found in 1,500 litres of water samples. They turned up more than a million new genes. The researchers are now retracing the voyage of HMS Beagle, the ship on which Charles Darwin sailed around the world.