The Rosetta spacecraft has successfully released its on-board lander, Philae, which has now begun a seven-hour descent to become the first object to land on a comet.

Just after 8pm AEST, the European Space Agency's ground control staff received the crucial signal that confirmed Philae, a 100-kilogram science lab, had detached from its mothership about 22.5 kilometres above the comet's surface.

At touchdown: Ice screws and harpoons will lock Philae to the comet's surface. Credit:ESA

It takes 28 minutes and 20 seconds for messages from Rosetta to travel 500 million kilometres back to Earth.

Australian avionics engineer Warwick Holmes, who helped build Rosetta, was ecstatic when he heard the ejection had worked successfully.