The latest attempts to contact the British Mars lander Beagle 2 have drawn a blank and the mission team accept the small probe is now probably lost.
Will there be "pups" of Beagle?
Attempts by the Mars Express orbiter to hail Beagle at the weekend failed.
The mission team has now started to look at what might have gone wrong and a board of inquiry will also be set up by the European Space Agency (Esa).
"Let's not grieve," said the project's lead scientist, Professor Colin Pillinger. "Let's look to the future."
Professor Pillinger was brieifing reporters in London on the latest efforts to track down the "pocket watch" lander.
"We haven't found Beagle 2, despite three days of intensive searching," he said. "Under those circumstances, we have to begin to accept that, if Beagle 2 is on the Martian surface, it is not active."
Confirmation that Beagle really is dead will come after one last option has been pursued.
This involves sending the lander a command via the US Mars Odyssey orbiter telling it to reboot its computer.
If the probe is still intact on the Martian surface and capable of receiving the message, it could just kick-start the Beagle into communicating. But Professor Pillinger told reporters it was a long shot.
"It is very much a last resort. We will be asking the American Odyssey spacecraft [team] ...whether they will send an embedded command - a hail to Beagle with a command inside it.
The Lovell dish at Jodrell Bank could not find Beagle
"If it gets through, it will tell Beagle to switch off and reload the software. We are now working on the basis that there is a corrupt system and the only way we might resurrect it is to send that command.
"We can also ask Mars Express to send that command. However, they cannot send it probably until the 2 or 3 February," he added.
But the repeated failure to contact Beagle using three orbiters and Earth-based radio telescopes means the chances of getting a signal from the craft now look very slim, and the Open University planetary scientist said it was really time to put people "out of their misery".
The mission team is now focussing on the possible reasons for failure, including the parachute and landing bags not working properly or the probe falling into a crater.
A key to this investigation will be getting an image showing Beagle or its landing components on the surface.
Esa's inquiry will take some time to set up. "It takes time to get the experts together to sit on it," said Professor Pillinger. "There's nothing sinister in it. All space missions have a review board when there's a
malfunction... and if Esa didn't call for it, we would."
The head of science at Esa, Professor David Southwood, told BBC News Online: "We will be setting up a commission of inquiry to consolidate what we did right and to find out what went wrong.
"Mars has something of a jinx for spacecraft. There is a long history of investigations of failed Mars missions. We want to make sure we add to the lessons learned."
Professor Pillinger and his colleagues are keen to send "pups" of Beagle to Mars in 2007. They believe the experiments they sent on the probe to look for Martian life were first class and deserve a second chance.
But before any space agency would even consider unleashing a pack of such probes on Mars, it would want to be sure the problems that seem to have blighted Beagle have been identified and can be designed out.
"We are dedicated to trying to re-fly Beagle 2 in some way, shape or form," said Professor Pillinger. "We will now begin to look at all the aspects of Beagle with a view to deciding what was good and what we would like to change and do differently in the future."