Rosetta harpoon glitch can't quell enthusiasm for another miraculous feat of science
A European spacecraft which made history by touching down on a comet may have failed to anchor itself firmly to the object's icy surface, scientists have revealed.
European Space Agency (ESA) mission controllers clapped, cheered and hugged each other after receiving confirmation that the Philae probe had landed.
Among those delighted with the news was Professor Alan Fitzsimmons from Queen's University Belfast's Astrophysics Research Centre. He and his colleagues have been studying the comet and waiting for the landing for more than a decade.
But celebrations were tempered by the later discovery that the probe's two harpoons had not fired to fasten the craft down in the ultra-low gravity.
Scientists now think the probe may have bounced after first coming into contact with the surface.
Philae lander manager Dr Stephan Ulamec said: "Maybe today we didn't just land once; we landed twice."
Despite the mishap, the probe appears to be operating as intended. However, there have been gaps in its radio link with the orbiting Rosetta mother ship.
The lander is also equipped with ice screws on the tips of each of its three legs which may help to keep it grounded. Speaking at the mission control centre in Darmstadt, Germany, Dr Ulamec said: "What we know is we touched down. We had a very clear signal there and we also received data from the lander.
"That's the very good news. Not so good news is that the anchoring harpoons apparently did not fire.
"We're still don't fully understand what has happened
"Hopefully we are sitting there in safety in a position slightly different to the original landing and we can start a scientific sequence."
The comet, 67P/Churyumov-Gerasimenko, is a 2.5 mile-wide rugged lump of ice and dust hurtling through space at around 40,000mph. Merely to land on an object more than 300 million miles away after a 10-year, four billion-mile journey through space has been hailed as one of science's greatest ever achievements.
A radio signal confirming the landing was received by scientists at 4.03pm UK time after taking almost 30 minutes to travel the 316 million miles to Earth. It is the first time any man-made object has made a controlled landing on a comet.
Success was never certain. The comet is strewn with deep pits, towering cliffs and peaks, craters and boulders - some the size of houses. Some time before the landing there was a heart-stopping moment when the probe's active descent system, which uses thrust to prevent the craft bouncing away into space, could not be primed.
Another glitch was fixed in time-honoured tradition - by switching Philae's computer off and on again.
Scientists hope the £1bn mission will yield valuable information about the origin of the solar system, the Earth, and possibly life. Comets bombarded the Earth early in its history, helping to fill the seas with water and depositing complex organic chemicals which may have contributed to the birth of living things.
A British-led instrument, Ptolemy, will be used to analyse the composition of samples in the craft's onboard laboratory.
After the landing, Rosetta's colourfully tattooed British project scientist Dr Matt Taylor said: "To see this mountaineering effort, that we've descended a lander to the surface of a comet; I can't put words to it.
"We did a good job. I knew we were going to do it."