They've been waiting for 10 years, and today the Rosetta spacecraft finally arrives at its destination - an icy comet more than 300 million miles from Earth.
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Scientists at Queen's University Belfast who have spent years preparing for the arrival of the craft at comet 67P/Churyumov-Gerasimenko are on tenterhooks as they wait for the touchdown signal to reach Earth this afternoon.
Professor Alan Fitzsimmons from the Astrophysics Research Centre at QUB and his colleagues have been studying the comet from afar for more than a decade and today they hope to get a close-up look at the cosmic body.
"I'm excited and anxious for all the hundreds of scientists, technicians and engineers that have been working on this mission for over a decade," he said.
"What we've been doing over the past few years is observing the comet from Earth, measuring the properties of the comet before the spacecraft gets there, how big it is, how fast it's rotating and so on. Rosetta is now very, very close to the comet, at times less than 10km, and we have a very detailed view but we can't see what happens to material beyond that distance."
The €1.3 billion (£1bn) Rosetta spacecraft was launched in 2004, and has spent a decade manoeuvring to rendezvous with the comet. Performing three fly-bys of the Earth, one of Mars and also passing close to two asteroids, it finally reached comet 67P on August 6 this year. Now both are racing through space together at over 60,000km/h.
Professor Fitzsimmons has just returned from Chile, where he used the world's most powerful telescopes to perform a final reconnaissance of the comet. Some of his colleagues include former Queen's students now working on the mission.
"We have waited over 10 years for this day, but with the comet being over 317m miles away, all we can do now is cross our fingers and hope," Professor Fitzsimmons said.
"The Rosetta mission realises the ambition of mankind to explore our origins, and discover what is out there.
"It demonstrates that the European Space Agency plays a major role in the scientific exploration of our Solar System, and Queen's is part of that effort."