A European spacecraft that broke off contact as it attempted to land on Mars may have jettisoned its parachute too early, investigators believe.
Mystery surrounds the fate of Schiaparelli, which began its six-minute descent at 3.42pm Irish time on Wednesday.
Scientists know that its heat shield functioned properly and its parachute deployed as planned at an altitude of 10km (6.8 miles).
But something went wrong around the time the craft was due to eject its parachute and fire up three clusters of retro rockets before landing.
A statement from the European Space Agency (ESA) said: "The data have been partially analysed and confirm that the entry and descent stages occurred as expected, with events diverging from what was expected after the ejection of the back heat shield and parachute.
“This ejection itself appears to have occurred earlier than expected, but analysis is not yet complete.”
The nine retro rockets, which should have slowed the probe’s descent to less than 4.3mph before the craft dropped the final 198.12cm (6.5ft) to the ground, were thought to have switched off “sooner than expected”.
The evidence points to Sciaparelli hitting the ground too fast and too hard, though this is yet to be confirmed.
Probe’s data stream cut off
Andrea Accomazzo, head of ESA’s planetary operations, said the probe’s data stream was cut off “in the order of 50 seconds” before the planned touchdown.
Speaking at ESA's mission control centre in Darmstadt, Germany, he said: "Unfortunately we're not in a position yet, but we will be, to determine the dynamic condition at which the lander has touched the ground. Then we will know if it has survived structurally or not."
He said the data showed the retro rockets firing for three or four seconds, “a time much shorter than we were expecting”.
Schiaparelli was only the second probe ESA has attempted to land on Mars. The first, Beagle 2, also suffered a radio blackout after detaching from its Mars Express mothership on Christmas Day 2003.
Anxious minutes of waiting turned into hours and days until scientists finally had to admit that the British-built craft was lost.
It was not until last year that scientists discovered the probe on the surface of Mars.
Satellite images suggested two solar panels had failed to deploy, blocking its communications antenna.
ESA scientists refuse to be disheartened about Schiaparelli, pointing out that its prime function was to test an untried landing system for a rover mission due to be launched in 2020.
ExoMars Rover will send a six-wheeled mobile laboratory built in the UK to the Red Planet to drill for soil samples and analyse them for signs of past or present life.
Orbital insertion a complete success
While Schiaparelli was plunging through the Martian atmosphere, its mothership, the ExoMars Trace Gas Orbiter, settled itself to circle the planet. ESA said the orbital insertion had been a complete success.
TGO will sniff the Martian atmosphere for trace gases including methane, which may have a biological origin.
ESA director general Jan Worner stressed that the aim of the Schiaparelli “test” was to obtain engineering data.
“We got the knowledge,” he said. “I’m happy. I think it is a big success.”
Former UK Space Agency chief executive David Parker, now director of human space flight and robotic exploration at ESA, said: “We have over 100kg of science instruments in orbit around Mars now so we’re ready to undertake really exciting science.”
As it fell through the Martian atmosphere, Schiaparelli was supposed to capture photos of the approaching ground.
The craft was designed to land on terrain containing rocks as high as 40cm (16in).
PA