After six years in space, Japan's Hayabusa-2 probe is heading home, but only to drop off its rare asteroid samples before starting a new mission.

The fridge-sized probe, launched in December 2014, has already thrilled scientists by landing on and gathering material from an asteroid some 300 million kilometres from Earth.

But its work is not over yet, with scientists from Japan's space agency JAXA now planning to extend its mission for more than a decade and targeting two new asteroids.

Before that mission can begin, Hayabusa-2 needs to drop off its precious samples from the asteroid Ryugu - "dragon palace" in Japanese.

Scientists are hoping the capsule will contain around 0.1 grams of material that will offer clues about what the solar system was like at its birth some 4.6 billion years ago.

The samples could shed light on "how matter is scattered around the solar system, why it exists on the asteroid and how it is related to Earth," project manager Yuichi Tsuda told reporters.

The material is in a capsule that will separate from Hayabusa-2 this Sunday, while it is some 220,000km above Earth and then plummet into the southern Australian desert.

The Royal Australian Air Force is monitoring the drop from its Woomera Range Complex.

The samples were collected during two crucial phases of the mission last year.

Artist's impression of the Haybusa-2 space probe

In the first, Hayabusa-2 touched down on Ryugu to collect dust before firing an "impactor" to stir up pristine material from below the surface. Months later, it touched down to collect additional samples.

"We may be able to get substances that will give us clues to the birth of a planet and the origin of life... I'm very interested to see the substances," mission manager Makoto Yoshikawa told reporters.

Protected from sunlight and radiation inside the capsule, the samples will be collected in Australia, processed, then flown to Japan.

Hayabusa-2 blasting off into space back in 2014

Half the material will be shared between JAXA, US space agency NASA and other international organisations, and the rest kept for future study as advances are made in analytic technology.

After dropping off its samples, Hayabusa-2 will complete a series of orbits around the sun for around six years, recording data on dust in interplanetary space and observing exoplanets.

It will then approach the first of its target asteroids in July 2026.

The mission extension comes with risks, including that Hayabusa-2's equipment will degrade in deep space, but it also offers a rare, comparatively cost-effective way to continue research.