Sydney engineer hails comet landing

The first successful landing of a spacecraft on a comet has turned science fiction into fact, says the Sydney engineer who helped build it.

Warwick Holmes helped with the space craft Rosetta, which just after 3am put a lander, Philae, on the surface of comet 67P/Churyumov-Gerasimenko.

It was the end of a 10-year mission chasing the 3.5km by 4.0km space body.

"We've turned science fiction into science fact today," Mr Holmes told the ABC on Thursday.

"It's been one of the most incredible results ever in space exploration history.

He said the landing will allow scientist to prove how water got to Earth in the first place when the planet was a red hot ball of molten rock with no surface water.

"Now, after it cooled down something happened, comet material came down and hit the earth again and they believe this has carried the water that has made the oceans," he said.

"We'll be able to prove definitively that the molecules on the surface are responsible for the formation of life on earth."

The 100kg Philae detached from Rosetta soon last night and travelled 22.5km to the comet's surface.

Mr Holmes, who is in Darmstadt, Germany, said photos were sent to Earth as Philae landed on the comet, some 500 million kilometres from earth.