Mission controllers said they were in the dark about the fate of the Schiaparelli probe, which is believed to have touched down on Wednesday after a seven-year journey.
"We are not in a position yet to determine the dynamic condition at which the lander touched the ground," said Andrea Accomazzo, ESA's head of solar and planetary missions.
Scientists said they had received data showing the lander's heat shield and parachutes had deployed successfully.
But it was unclear what happened in the final seconds before the probe landed on the Red Planet, and no data had yet been received from the surface, they said.
One possibility under investigation is that the parachute may have been ditched too early as the craft came in to land.
Scientists do not know whether Schiaparelli, a disc-shaped 577kg (1,272lb) probe, was still in one piece.
Further data analysis is required to "know whether it survived structurally or not," said Mr Accomazzo, during a briefing at mission control in Darmstadt, Germany.
The craft was sent to Mars from Earth in a journey that spanned hundreds of millions of miles. It was the second European attempt to land a craft on the Red Planet.
The ExoMars mission's main objective is to look for signs of life on Mars.
But just overcoming the notoriously tricky Martian atmosphere - too thin to rely on a parachute alone and too thick to reliably use thrusters - would be seen as a major achievement.
For the space agency the landing is a "technology demonstrator" - a test of the descent system it hopes to use in 2020 to put a robotic rover on the surface.
The head of ESA, Jan Woerner, said the mission should still be considered a success because the probe sent a vast amount of data back before going silent.
"Following yesterday's events we have an impressive orbiter around Mars ready for science and for relay support for the ExoMars rover mission in 2020," he said.
"Schiaparelli's primary role was to test European landing technologies. Recording the data during the descent was part of that, and it is important we can learn what happened, in order to prepare for the future."