NASA scientists failed again yesterday to break the ominous silence of the Mars Polar Lander - for the fifth time in 48 hours - and acknowledged the possibility that the probe did not survive the landing.
"Our confidence is less and less that we landed successfully," said project manager Mr Richard Cook. Mr Cook said the team - which he described as "getting more frustrated and more tense about this" - would continue to try various ways to communicate with the craft, all of which would be completed by tomorrow.
"Once we are done with these, we are really at the point of diminishing returns. After Tuesday we will have to question whether or not the lander entered [the Martian atmosphere] and landed successfully," he said.
Following the loss of the Mars Climate Orbiter in September due to human error, the loss of the current mission would be a crushing blow to NASA's "better, cheaper, faster" solar exploration programme and might lead to new criticism of attempts to conquer Mars on the cheap.
But Mr Cook defended the concept, pointing out that NASA would be sending probes to Mars every two years. "This would be much more painful if it was the only mission for the next 10 years. We have missions every two years. We can learn from our mistakes. We have to be determined to go and not give up when this kind of thing happens."
The $165 million probe was supposed to use its ultra high frequency antenna to make contact with the Mars Global Surveyor satellite orbiting the planet during a brief, six-minute communications window, but it remained silent, as it has since Friday, when it was scheduled to land on Mars.
Yesterday marked the first time scientists had tried to get the craft to use its UHF antenna, which is not powerful enough to communicate directly with Earth but is capable of sending a stream of data to the orbiting surveyor for relay to Earth.
The primary mission was to look for water which scientists believe is trapped just underneath the Martian surface. The probes were to dig about 70 cm under the surface and take soil samples which they would test for water content by heating them in tiny ovens to detect vapour. Water could give clues as to whether there was ever life on Mars, even in its most primitive form.