'We're quite excited' - Nasa

Malin and co-author Dr Kenneth Edgett enjoy the fun

There had been all sorts of stories flying around on the net for two days. Some had suggested that debris from the Mars Polar Lander had been discovered. Others even said life itself had been discovered on Mars.

And then Nasa hit us with it: channels in the flanks of Martian craters that were almost certainly formed by recent, running water. Okay, so recent can mean within the last one million years, but it could mean yesterday as well. And that really is exciting.

This is a fun press conference as opposed to some of them I've been doing lately

Dr Ed Weiler, Nasa

The news conference called at Nasa's Washington headquarters worked first to cool down the speculation surrounding the announcement.

"We've certainly not found a hot tub with Martians swimming in it," said Dr Ed Weiler, with the office of space science at Nasa.

However, Dr Weiler said, if it could be proven that these features were caused by water near the surface of Mars, "it would have profound implications for the prospect of life on Mars".

One of the images released at the conference showing deep channels descending a Martian crater wall

And, "if we find life - past or present - that would have profound implications that we are not alone," he said.

Dr Weiler was so enthusiastic about the discovery he waved his arms around and sent the microphone in front of him flying.

"I'm actually excited about this. This is a fun press conference as opposed to some of them I've been doing lately," he said.

Last year, Nasa's Mars programme came under intense scrutiny after back-to-back, high profile failures of missions to the Red Planet. Dr Weiler found himself as the lead defender of the space agency in the face of stinging criticism. Now, he had good news.

Dr Weiler said the discovery would not only give a boost to unmanned missions to Mars but also to the prospects for a manned mission some time in the future.

Dr Michael Malin, who co-authored the scientific paper in which the water claims were contained, said: "If water is available in substantial volumes in areas other than the poles, it would make it easier for human crews to access and use it."

Even Nasa chief Dan Goldin had something to smile about

Water near the surface could be used not only for drinking but also to create breathable air and to extract hydrogen and oxygen for rocket fuel.

Manned exploration was clearly on the minds of the two authors. When they presented an illustration outlining how groundwater on Mars could create the features they had observed, they said they had thought about including pipes pumping water from the cliffs to a base on the valley floor.

They then quipped that it might not be drinkable on the first sip. They admitted that factors other than water might have caused the formations, but Dr Malin added that they might not have the definitive answer "until someone goes up to a cliff with a pick and a shovel".