Japan's space agency said Tuesday its Hayabusa2 probe is now homeward bound after activating its main engines following completion of its mission to collect samples from an asteroid.

The probe is set to travel around 800 million kilometers to deliver the samples from the Ryugu asteroid to Earth in November or December next year, according to the Japan Aerospace Exploration Agency.

Hayabusa2 left the asteroid on Nov. 13, five years after its launch, and tested its ion engines from Nov. 20 to Monday before beginning the return journey.

(Supplied computer graphic shows image of Hayabusa2 space probe and the Ryugu asteroid.)
[Photo courtesy of JAXA]

If organic matter is found in the samples, it could lead to a potential breakthrough in looking at the formation of the solar system and life on Earth.

Once the samples are released, the probe will go on another mission. The agency has said it will consider releasing the rock samples at a height equivalent to the distance between Earth and the Moon as an option to avoid the Earth's gravitational pull and disruption of the probe's trajectory.

Launched in December 2014 from the Tanegashima Space Center in southwestern Japan, Hayabusa2 reached Ryugu in June last year. The asteroid's subsurface rock, unaffected by solar flares, is believed to have retained the same state since the solar system was formed 4.6 billion years ago.

The probe touched down on Ryugu twice and succeeded in collecting the first-ever asteroid subsurface samples after creating an artificial crater by shooting a copper projectile at the asteroid.

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