The splash of fresh water has been heard on Mars, raising the possibility that it may one day prove home-from-home for colonists. Meticulous examination of images taken by Mars Global Surveyor show gullies, channels and fans of debris identical to those produced on Earth by flowing water, say Michael Malin and Kenneth Edgett of Malin Space Science Systems in San Diego, California.

“These gullies could be a million years old, or they could have formed yesterday,” says Dr Malin. But only about 150 of the more than 25,000 images taken by the satellite show the traces and an Australian geologist, Nick Hoffman of LaTrobe University in Melbourne, doubts they have anything to do with water. He says that debris swept along by carbon dioxide formed the gullies, and that if water exists on Mars, it is deep below the surface.

The flows Dr Malin envisages would be like pyroclastic flows from volcanoes on Earth, which can plunge down a mountainside at hundreds of miles an hour, carrying dust and debris with them.

A new Mars explorer, to be launched in June 2003, could help settle the argument, assuming it does not meet with the same fate as the US space agency Nasa’s last two Mars missions. The plan is to land the new rover in an area that looks like a dry lake bed and cruise around in search of evidence that it once held water.

BIRDS ARE not descended from dinosaurs, according to Russian and American scientists, but from a feathered lizard which glided through the trees 220 million years ago.

The discovery was made, oddly enough, in a Kansas City shopping mall, where palaeontologists John Ruben and Terry Jones of Oregon State University ad gone to give a lecture in support of a travelling Russian fossil exhibit. “We took one look at these fossils and realised immediately this was a very old animal with feathers,” said Dr Ruben. “We stayed up all night in a vacant store in the mall to study it.”

The reptile was an archosaur, a group ancestral to both birds and dinosaurs, and it had true flight feathers at least 75 million years before Archaeop-teryx, the first true bird.

The discovery is manna from heaven to Professor Alan Feduccia of the University of North Carolina, an expert on the evolution of birds who has never accepted the now-fashionable theory that they are the descendants of dinosaurs. The new discovery, called Longis-quama insignis, had bird-like features long before dinosaurs even appeared.

THE FIRST trials start in Oxford this autumn of an Aids vaccine designed specifically for Africa. Developed by scientists from Oxford and Nairobi universities, the hope is that the vaccine will stimulate a strong immune response against the strains of HIV prevalent in Africa. The first trials, on 18 healthy volunteers, will be designed simply to see that it is safe.

The vaccine was announced at the 13th International Aids Conference in Durban, which also heard evidence that the success of the triple-drug cocktail which has slowed Aids-related deaths in the US and Europe may be threatened by growing drug resistance. Professor Brian Gazzard of Chelsea and Westminster Hospital in London estimates that up to 5 per cent of his patients may already be resistant to all three drugs in the triple therapy. Studies in Italy and the US have put the proportion as high as 30 per cent.

Nigel Hawkes is science editor of The Times