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Darmstadt - Europe's robot probe Philae did not anchor to comet 67P/Churyumov-Gerasimenko after landing harpoons failed to fire, but still managed to send home lots of data, the European Space Agency (ESA) said Wednesday.
"The lander is not anchored to the surface," Philae lander manager Stephan Ulamec told reporters at ground control in Darmstadt, Germany.
"We still do not fully understand what has happened," he added.
Fluctuations in radio signals suggested Philae had either landed "in a soft sandbox" or had gently rebounded from the surface and returned to it.
"So maybe today we didn't land once, we even landed twice," he quipped.
Several instruments onboard Philae had already sent back "plenty of data," he said.
"Hopefully, we are sitting there on the surface at a position slightly different to the original landing and can continue our science."
As expected, the radio link between Philae and Rosetta was broken when the orbiter went beyond the lander's horizon, said Ulamec.
More would be known when communications return on Thursday, he added.
The 100kg lander separated from its mothership, Rosetta, after a trek lasting a decade and covering 6.5 billion km.
Philae was designed to settle down at a gentle 3.5 kilometres per hour, firing two harpoons into a surface that engineers hoped would provide sufficient grip while the robot conducts experiments with 11 scientific instruments.
Envisaged tests include drilling through the comet surface and analysing the ice and dust for chemical signatures.
According to a leading theory, comets pounded the fledgling Earth 4.6 billion years ago, providing it with carbon molecules and precious water - part of the toolkit for life.
In Toulouse, France, astrophysicist Philippe Gaudon, who heads the Rosetta mission at French space agency CNES, said it would be difficult for Rosetta to carry out drilling if it was not anchored.
"However, Philae has not tipped over and seems to be stabilising," Gaudon said.
"And a certain number of instruments are continuing to operate, mainly for measuring temperature, vibration, magnetism and so on."
