US Lander Falls Silent

Spirit, the six-wheeled rover that 19 days ago made a triumphant touchdown on Mars, has fallen mysteriously silent.

Late last night, the robot geologist had failed to transmit any coherent message for more than 24 hours. Nor could Nasa's mission controllers in Pasadena make it respond to commands.

The only "noise" from the lander since Wednesday has been sporadic, meaningless data transmitted across 100m miles of space.

"This is a serious problem. This is an extremely serious anomaly," project manager Pete Theisinger told Associated Press.

Communication is at the heart of every space mission: if it fails, then to all practical purposes, the mission is lost.

In the past 40 years there have been 36 attempts to explore the red planet. Ultimately, two out of three have failed. Some missions perished on the launch pad, some were lost in space, some fell silent as they neared their destination. In one fateful 10-week period in 1999, Nasa lost all four of its spacecraft over the arid deserts of Mars.

British scientists still hope to hear from their baby, Beagle 2 - the tiny lander reached Mars on Christmas Day but since then has failed to send a message home - although the chances must by now be small. They have, at least, been able to cheer Beagle's European mothership Mars Express, which has settled into a polar orbit around Mars and begun to return the first of what they hope will be dramatic new data about the landscape, mineral makeup and atmosphere of the Earth's smaller, colder neighbour.

Spirit was the first part of an ambitious $820m (£450m) US mission to take a close look at the stony landscape of Mars. It landed in the Gusev crater, a large rocky basin south of the Martian equator, with a set of geological tools, a stereoscopic camera at roughly human eye level, and a remit to look for evidence of vanished seas, lakes or rivers.

A second identical rover, Opportunity, is to touch down on Sunday on a plain called Meridiani, a region rich in the mineral haematite, linked on Earth to water deposits. If Mars once had flowing water, it must also have supported a denser atmosphere - and even perhaps life. Both the Beagle and Spirit landers were part of a systematic, international search for life on Mars.

Spirit made what seemed a textbook landing on January 4, sending pictures and data promptly back to jubilant controllers on Earth. But the joy may prove shortlived. On Wednesday morning, the rover had been preparing to examine its first Martian rock, a sharply angled piece of stone a few yards from its landing platform. Since then, it has sent back a few beeps and default signals.

Scientists worked through Wednesday night and yesterday, checking the possibility of a major power failure, a software fault or a memory corruption. If the software is awry, Nasa can fix it from Earth by beaming patches across more than 100m miles of space. But if the problem lies with the rover's hardware, the situation would be far more grave.

"Yes, something could break, something certainly could fail. That's a concern we have - that's quite a serious event," Dr Theisinger said.

They were pinning their hopes on yet another attempt to contact the rover at 4.30am this morning. But they could offer no explanation for the loss of contact with Spirit.