The Mars Odyssey spacecraft failed to pick up a signal from the Beagle probe when it flew over the landing site on Christmas morning.
By Helen Briggs
BBC News Online
There was disappointment on the faces of British scientists who had waited all night for news of their "baby".
But nobody is giving up yet. One of the biggest radio telescopes in the world at Jodrell Bank in Cheshire in northwest England will come online at 2200 GMT to listen out directly for Beagle's call sign.
"It's like looking for a needle in a haystack," says Beagle scientist Andrew Coates of University College's Mullard Space Science Laboratory.
Nobody is giving up just yet
"Even if we don't get the signal tonight we will still have hope."
If Jodrell bank does pick up Beagle's call sign it will be very good news indeed.
It will show that the tiny spacecraft has survived not only the landing but the first Martian night, when temperatures plunge.
Hearing nothing on the evening of Christmas Day will prolong the agony.
Mission scientists will have to wait until 1815 GMT on 26 December for Mars Odyssey's next flight over the landing site.
In the meantime, they are contemplating various scenarios - Beagle could have landed in a crater or next to a boulder where it is unable to point its antenna at the sky.
It may have missed its landing site altogether and be out of range of Odyssey's flight path.
And there is a slim chance that it cannot "talk"' to the US space agency's (Nasa) Mars Odyssey at all.
Beagle was designed to send data via its mothership Mars Express which will
not be in position to search for Beagle until early in the New Year.
Scientists at Leicester University's Lander Operations Control Centre are looking at the possible explanations.
"The show isn't over by any means," says head of space research George Fraser. "We just have to be patient and wait to see how things unfold."
There is, of course, another more grim scenario. As Ian Wright, of the Open University in Milton Keynes, puts it, Beagle may have "crashed and burned".
This is an eventuality the Beagle team refuses even to contemplate at this stage. Nevertheless, the historic odds of a successful landing on Mars are low.
There has long been talk of a galactic ghoul that reaches out from the asteroid belt and snacks on Mars spacecraft.
One consolation is that the European Space Agency's (Esa) Mars Express appears to have gone into orbit around Mars without a hitch.
The landing could have damaged the probe
The spacecraft will search for water, ice and key chemicals buried under the Martian surface - a key part of the mission.
In early January, if all else fails, it will be able to search the planet for signs of Beagle's parachutes and airbags.
In the meantime, mission scientists will be hoping that Esa's mascot in its control room in Darmstadt, Germany - a stuffed Beagle dog wearing shades to protect against solar flares - will appease the dreaded galactic ghoul.