By Paul Rincon
BBC News science reporter
The launch of Europe's first mission to Venus, due to have taken place next Wednesday, has been postponed.
The European Space Agency (Esa) has not yet announced a new date for the launch, only that it will be delayed by "several days".
The probe is to blast off aboard a Russian Soyuz rocket from Baikonur Cosmodrome in Kazakhstan.
It will slip into orbit around Venus next year, using science instruments to study the planet from space.
Esa said the delay had been prompted by the discovery that insulation from the rocket launcher had contaminated the Venus Express spacecraft.
"The satellite is contaminated, so they will have to dismantle and re-mount it again," a spokesperson for the space agency told the BBC News website.
Venus Express will also need to be cleaned up to remove any trace of the insulation.
The contaminating material could have come from the rocket's upper "Fregat" stage, which boosts Venus Express into its interplanetary flight trajectory, or from the fairings, which protect the spacecraft during launch.
The spacecraft will carry out the first global investigation of Venus' atmosphere, to shed light on how the planet evolved its hellish climate.
Composed chiefly of carbon dioxide, Venus' atmosphere generates intense greenhouse warming, whereby trapped solar radiation heats the surface of the planet to an average of temperature of 467C.
Experts think Venus could teach us more about how the Earth's climate will respond to the release of greenhouse gases resulting from human activities.
After separation of the Soyuz rocket's three lower stages, the upper "Fregat" stage with the orbiter mounted on top enters a sub-orbital trajectory.
After two burns, Fregat will launch the spacecraft into an escape trajectory that takes it directly to Venus.
In about five months, Venus Express will reach its target and enter an elliptical polar orbit around our nearest planetary neighbour.