Philae, a probe dropped from the Rosetta spacecraft, has successfully descended on a comet but its harpoons did not fire, the European Space Agency's (ESA) ground controllers say.

An hour after the landing, the ESA said that while the probe is on the surface and is functioning, its harpoons anchors did not shoot and they were looking into the issue.

The 100kg robot lab, carrying 10 scientific instruments, landed at about 15:30 GMT on Wednesday on 67P/Churyumov-Gerasimenko, with a confirmation signal sent to Earth about half an hour later [at about 16:00 GMT].

ESA scientists waiting for the signal at mission control in Darmstadt, Germany, erupted in cheers on Wednesday once they received confirmation of the successful landing.

"We are the first to have done that, and that will stay forever,'' said ESA director-general Jean-Jacques Dordain.

Al Jazeera's Tarek Bazley explains Europe's space probe Philae

While further checks are needed to ascertain the state of the lander, the fact that it is resting on the surface of the speeding comet is already a huge success.

Al Jazeera's Tarek Bazley, reporting from Darmstadt, said that the mood at ESA was euphoric.

"Lot of people spend their careers on their missions...for them it was an amazing day," he said.

Bazley added that there was some confusion as to what happened and that the harpoons that were supposed to activate did not fire.

He went on to speak with Gerhard Schwehm, former mission manager on the Rosetta mission, who said that the lander is on comet and they could still fire the harpoons but said that "we have to see what happens".

Philae was placed on a trajectory on Wednesday towards 67P/Churyumov-Gerasimenko, a comet now more than 510 million km from Earth and racing towards the Sun at 18km per second.

Rosetta was launched in 2004 on a 6.5bn-km space trek that saw it enter 67P/Churyumov-Gerasimenko's orbit in August this year.

The spacecraft reached the comet - a 3km-by-5km rock discovered in 1969 - after a journey of 6.4 billion km as part of a mission that cost close to $1.8bn

Astrophysicists hope Philae will unlock knowledge about the origins of the Solar System and even life on Earth, which some believe may have started with comets "seeding" the planet with life-giving carbon molecules and water.

"By studying one in enormous detail, we can hope to unlock the puzzle of all of the others,'' said Mark McCaughrean, a senior scientific adviser to the mission.

Philae also tweeted its first image of the comet 67P, taken when it was 3km away from landing.

Source: Al Jazeera and agencies