By Jonathan Amos
BBC News Online science staff
The UK-led Beagle 2 team which tried to put a lander on the surface of Mars last year has published the findings of its own inquiry into what went wrong.
Supporters want another chance to fly Beagle's instrument package
The investigation looked at possible technical reasons for the loss of the probe and the lessons learnt which might benefit any future missions.
The team maintains its belief that a thinner than expected atmosphere may have thwarted a controlled landing.
The robotic laboratory was designed to search Mars for signs of life.
The last contact was an image of Beagle taken by its mothership, the Mars Express orbiter, on 19 December.
The £45m lander was scheduled to put down in a near-equatorial region of the planet known as Isidis Planitia on 25 December.
Despite many attempts to locate the probe - by overflying spacecraft and Earth-based telescopes - no sign of it, not even any wreckage, has been detected.
"The real reason for doing this [report] was to put the analysis down, to do a critique of what we did, to put those lessons learnt down for future possibilities," Dr Mark Sims, Beagle 2's mission manager, told the BBC.
"I hope that Europe and the UK will go back to Mars fairly quickly."
The internal inquiry has led to a very technical 288-page document, which goes into every aspect of the mission's design and execution.
It concludes: "No definitive cause of the failure can be identified due to lack of data - radio, telemetry or visual."
Unlike the successful US space agency rovers - the mobile "geologists" Spirit and Opportunity - Beagle had no means of contacting Earth from the moment it left its mothership, to the point it was supposed to open its antenna on the Martian surface.
Had it been able to feed back some information as it raced into the Martian atmosphere at 5km/s, the Beagle team might now have a better idea of which aspect of the entry/descent/landing sequence went wrong.
As it is, the scientists and engineers are left with the suspicion that their probe fell foul of a Martian atmosphere that was thinner than the one for which they had planned.
Subsequent analysis of data obtained by Mars Express and the rovers indicates the planetary scientists still have much to learn about the behaviour of the Red Planet's air.
"It was very different to all the atmospheres that we had from the mathematical models," Beagle 2's chief engineer, Dr Jim Clemmet, said.
The last contact: Beagle seen moving away from Mars Express
A thinner atmosphere or even air pockets would have resulted in the spacecraft travelling too fast as it approached the surface; its parachute and air bags would have failed to open with sufficient time to allow for a soft landing.
It is possible, the report says, Beagle hit the surface at some 200m/s, gouging a 5-6m-wide crater. The probe would have been totally destroyed.
But no photographic evidence for such a crater in the landing ellipse has yet been found and until it is, the team cannot really be sure what happened to their robot.
"My nightmare is that Beagle is sat there on the surface of Mars still trying to talk to us and, for the sake of a broken cable, it's not," said Dr Sims.
A European Space Agency (Esa) report in May said poor management of the mission should share some blame for its failure. It also said there should have been more testing of systems and components.
But Professor Colin Pillinger, Beagle's lead scientist, is robust in his defence of the team. "I will defend to my dying breath the management of this project," he said.
"I said we could have done more testing; in space missions you can always do more testing... but you can spend an infinite amount of money, do every test you like, you still can't eliminate all the risks of landing on Mars."
As with the Esa commission of inquiry, there is a recognition that it was a mistake to treat Beagle as an add-on "instrument" to the main Mars Express mission. It is a model no one wants to repeat.
"Appropriate priority including funding, schedule and resources must be given to a lander in any future mission," the internal report says.
Professor Pillinger has asked the Americans if they can help with a follow-up
The team hopes that somehow Beagle's instrument package - universally agreed to be innovative - can be flown again.
Professor Pillinger has asked the US space agency if it would think about incorporating a Beagle payload into its 2009 Mars Science Laboratory - a large rover mission that would be dropped on to the surface by a "skycrane".
"[They could] take Beagle to Mars, leave it on the surface and drive away to carry on their own mission.
"If Nasa really wanted to get the benefit out of that they could use their rover to pick up samples to give to Beagle. If they were inclined, they could also come back and move Beagle.
"All this would be good practice for when anyone wants to bring back samples to Earth."