Europe's Schiaparelli lander did not behave as expected as it headed down to the surface of Mars on Wednesday.
Telemetry data recovered from the probe during its descent indicates that its parachute was jettisoned too early.
The rockets it was supposed to use to bring itself to a standstill just above the ground also appeared to fire for too short a time.
The European Space Agency (Esa) has not yet conceded that the lander crashed but the mood is not positive.
Experts will continue to analyse the data and they may also try to call out to Schiaparelli in the blind hope that it is actually sitting on the Red Planet intact.
In addition, the Americans will use one of their satellites at Mars to image the targeted landing zone to see if they can detect any hardware. Although, the chances are slim because the probe is small.
For the moment, all Esa has to work with is the relatively large volume of engineering data Schiaparelli managed to transmit back to the "mothership" that dropped it off at Mars - the Trace Gas Orbiter.
This shows that everything was fine as the probe entered the atmosphere. Its heatshield appeared to do the job of slowing the craft, and the parachute opened as expected to further decelerate the robot.
But it is at the end of the parachute phase that the data indicates unusual behaviour.
"We cannot resolve yet under which, let's say, logic that the machine has decided to eject the parachute. But this is definitely far too early compared to our expectations," Andrea Accomazzo, the head of operations for Esa's planetary missions, told BBC News.
Not only is the chute jettisoned earlier than called for in the predicted timeline, but the retrorockets that were due to switch on immediately afterwards are seen to fire for just three or four seconds. They were expected to fire for a good 30 seconds.
In the downlinked telemetry, Schiaparelli then continues transmitting a radio signal for 19 seconds after the apparent thruster shutoff. The eventual loss of signal occurs 50 seconds before Schiaparelli was supposed to be on the surface.
Many scientists here at mission control have taken all this information to mean one thing - that the probe crashed at high speed. It is likely it went into freefall a kilometre or two above the surface.
Officially, though, Esa experts say they cannot at this stage fully interpret what happened until a velocity profile for the probe is properly reconstructed.
Once that is done, a match can be made against known events and their predicted altitudes. It ought then to be possible to gauge with some confidence whether Schiaparelli did indeed hit the ground at a catastrophic speed.
Landing on Mars is always a daunting prospect.
It is necessarily a high-speed approach that has to be got just right or the spacecraft runs the risk of smashing into the ground.
If the robot is later confirmed as lost, it will obviously be a major blow to Esa which suffered the disappointment of the Beagle-2 lander's failure at Mars in 2003.
But officials here have tried to emphasise Schiaparelli's role as a technology demonstrator - a project to give Europe the learning experience and the confidence to go ahead with the landing on Mars in 2021 of an ambitious six-wheeled rover.
This future vehicle is expected to use some of the same technology as Schiaparelli, including its doppler radar to sense the distance to the surface on descent, and its guidance, navigation and control algorithms.
What will concern commentators is that the budget for the rover is not yet secure. It is short by about 300m euros. If Schiaparelli is indeed lost, Esa officials may find themselves having to work harder to explain to member states why the extra investment remains worthwhile.
The agency's director-general, Jan Woerner, was bullish, however. The achievement of getting the TGO into a parking orbit at Mars to do several years of atmospheric study, combined with the retrieval of engineering data from Schiaparelli's descent, would, he said, play well with Europe's space ministers when they came to make decisions about the rover.
"I think they will see that this mission is a success. We have the function that we need for the 2020 mission, and therefore I think we don't have to convince them - we just have to show them. The results are obvious," he told reporters.