Rosettaâ€™s probe, Philae, has successfully landed on its comet 67P/Churyumov-Gerasimenko. After a daring seven-hour descent, the probe has made space history by becoming the first ever craft to land on a comet.
In an emotional speech, Esa director general Jean-Jacques Dordain said: â€œItâ€™s a big step for human civilization.â€
The confirmation of the landing was relayed via Rosetta to Earth and picked up simultaneously by a ground station in MalargÃ¼e, Argentina and Madrid, Spain, before being confirmed in Darmstadt.
â€œEsa and its Rosetta mission partners achieved something extraordinary today,â€ said Dordain.
â€œOur ambitious Rosetta mission has secured another place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a probe to a cometâ€™s surface.â€
â€œAfter more than 10 years travelling through space, weâ€™re now making the best ever scientific analysis of one of the oldest remnants of our solar system,â€ added Alvaro GimÃ©nez, Esaâ€™s director of Science and Robotic Exploration.
â€œDecades of preparation have paved the way for todayâ€™s success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration.â€
However, while the lander has touched down on the comet using its harpoons, scientists said that it had not yet deployed its anchors which meant that it was not completely attached to the surface.
The surface was much softer than they expected, so there were some concerns that it was not securely fixed on the comet â€“ although from a software point of view things seemed to be fine.
Engineers will attempt to fire the anchors again soon in order to keep Philae attached to the surface of the comet.
Speaking live on TV, Matt Taylor, project scientist of Rosetta, talked about the complexities of the mission.
â€œI said she was sexy but I never said she was easy,â€ he said, describing the thruster issue that worried scientists earlier today.
Despite this, after a four billion mile (6.5 billion km) journey, the probe successfully released Philae from its grip to land on the comet, travelling at 1 metre (40 inches) per second.
â€œWe are extremely relieved to be safely on the surface of the comet, especially given the extra challenge of the cometâ€s unusual shape and unexpectedly hazardous surface,â€ said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.
â€œIn the next hours weâ€ll learn exactly where and how weâ€ve landed, and weâ€ll start getting as much science as we can from the surface of this fascinating world.â€
Engineers were forced to endure a tense wait to discover whether the lander successfully grabbed onto the comet at 3.30pm GMT.
Ahead of the landing, Rosetta captured several images of Philae during its daring mission using its Osiris camera.
The separation of Philae from Rosetta was confirmed at 9.03am GMT today, and just after 11am GMT mission control in Darmstadt, Germany received a signal confirming the lander was working.
Throughout the day, the lander has transmitted data and images back to Earth.
â€œEverything looks really, really good,â€ said Philae lander manager Stephan Ulamec.
However, the success of the mission hung in the balance because Philae has a faulty thruster, which means it may have had to rely solely on harpoons to attach itself to the surface.
Whether or not it was able to make the thruster work in time has yet to be revealed by Esa. When Philae touched the surface of the comet it fired harpoons into the surface to keep it anchored there. To keep it attached to the surface a thruster at the top was mean to push it down as the harpoons fired.
But this morning, the thruster didnâ€t appear to be working. This meant the lander may have had to rely solely on its harpoons to stay attached to the surface. The harpoons may have grabbed the surface immediately and kept the lander anchored there. If they didnâ€t, the force of firing them could send it floating off into space.
â€œWeâ€ll need some luck not to land on a boulder or a steep slope,â€ said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center ahead of the landing.
The cold thruster would have been used to push Philae closer to the comet. Without it, Philae would have been forced to rely on its three landing screws and two harpoons to successfully attach itself to the surface.
However, if the thruster was reactivated and all went to plan, at touchdown a landing gear would have absorbed the force of the landing. Ice screws in the feet and a harpoon system locked to the cometâ€s surface and the thruster would have pushed it down into the surface to counteract the impact of the harpoon.
Before Philaeâ€s release, Esa said there was â€œno going backâ€.
â€œThis is the most difficult landing in space history, like landing a balloon in a city centre on a windy day with your eyes closed,â€ said Matthew Genge, a senior lecturer in Earth and planetary science at Imperial College London.
At 08.35am GMT the mission control team in Darmstadt, Germany, sent a command to release the Philae probe from Rosettaâ€s grip.
The probe was in free fall for during â€œseven hours of terrorâ€, before attempting to land on the icy surface of comet 67P/Churyumov-Gerasimenko at a site called Agilkia.
â€œWeâ€ll need some luck not to land on a boulder or a steep slope,â€ said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center, ahead of the landing.
Speaking to Astronomy Now, Head of Mission Operations Paolo Ferri said they had received both positive and negative readings from the thruster.
â€œWe donâ€t know whether the motor is working or not. We have inconsistent readings,â€ he said at the time.
William Shatner, who played Captain James T. Kirk in the TV series Star Trek, has wished the Rosetta team good luck ahead of the landing attempt in a video recorded by himself. â€œGood luck Rosetta, Philaeâ€s gonna land,â€ he says in the video. â€œI am so excited and I wish you such good luck. â€œGood wishes from all of us here in Los Angeles.â€
Shatner posted the video to his Twitter page, to which Esa responded: â€œThank you captain!â€
While the 83-year-old is known around the world as Captain Kirk from the fictional show Star Trek, he is also a big proponent of real space exploration. In the past he has spoken with Nasa and Esa on Twitter, occasionally â€œchecking inâ€ to see how the agencies are doing.
Back in August he tweeted: â€œHow is @NASA doing today?â€
Nasa responded: â€œ@WilliamShatner Good day, Captain. #ISS is in standard orbit and Commander Swanson has the conn. Hope youâ€re having a great weekend!â€
To which Shatner replied: â€œ@NASA Very good news!â€
Shatner played Kirk in Star Trek: The Original Series but also reprised his role elsewhere including in seven movies.