Scientists working on Europe's mission to hook up with a comet millions of miles from Earth have lost contact with the probe that has landed on its surface.

A statement on the blog of the Rosetta website says that the Philae lander craft was last heard from on July 9th.

Philae landed on the surface of Comet 67P/Churyumov-Gerasimenko on November 12th last year, beaming back pictures of the surface of a comet for the first time.

Shortly afterwards the craft went into hibernation but recently woke up again after its batteries were charged as the comet got closer to the Sun.

But since it went quiet again, experts at the European Space Agency (ESA) have been trying to work out what could have caused it to go silent.

The blog entry said: "One possible explanation being discussed at DLR's Lander Control Center is that the position of Philae may have shifted slightly, perhaps by changing its orientation with respect to the surface in its current location."

"The lander is likely situated on uneven terrain, and even a slight change in its position - perhaps triggered by gas emission from the comet - could mean that its antenna position has also now changed with respect to its surroundings."

Another possibility, the blog said, was that one of Philae's transmitters had developed a fault.

The team said that although its current status is "uncertain", they are continuing to prepare further tasks for it to carry out in the event that it wakes up.

The Rosetta probe, which is orbiting the comet and acts as a bridging station for the lander's transmissions, has been unable to get closer to the heavenly body's surface to try to make contact.

It is producing a bigger tail than it was in the earlier stages of its mission because it is moving closer to the Sun.

The comet, which was around 275 million kms from Earth and 193 million kms from the Sun on July 15th, is due to reach its closest point to the Sun - the perihelion - on August 13th.

Over the last few weeks, the ESA have been publishing a series of highly detailed pictures showing the landscape of the comet.