Officials said 12 out of 13 segments that comprise the first boom had deployed successfully, but segment 10 was not fully locked into place.

The Marsis radar has three booms which are designed to spring out of the spacecraft like a jack-in-the-box.

A space agency spokesperson said the anomaly did not threaten the mission.

Mission controllers were due to release the second antenna boom on Sunday, but following the discovery of the apparent kink in the first, a decision was taken to hold off.

Meetings are now being held to determine what implications the discovery has for deploying the second boom.

'Precautionary measure'

"It is more of a precautionary measure than anything else. It took us a long time to decide whether to go ahead with this and we are just being careful," said the spokesperson for the European Space Agency (Esa).

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"We have to look at whether [the boom segment] is very close to being completely locked or whether it is far from it."

The 20m-long (65ft) boom that was deployed on Wednesday forms one half of the Marsis (Mars Advanced Radar for Subsurface and Ionosphere Sounding) primary antenna.

The primary antenna will beam radio waves towards the surface of the Red Planet, some of which will penetrate the crust, probing the composition of the hidden layers of rock and possibly water.

It could help scientists identify underground reservoirs up to 5km (3 miles) down, which it is thought could provide a habitat for microbial life.

Deployment of the antennas was postponed for more than a year amid concerns that the boom could swing back and hit the spacecraft or get caught.

The experiment can function without its third, 7m-long (23ft) "monopole" boom, but this component will help investigators verify whether reflected radio waves are really coming from beneath the surface or simply bouncing off the surface further away from Mars Express.