The Japan Aerospace Exploration Agency (Jaxa) said the Hayabusa2 left its orbit around the asteroid Ryugu, about 180 million miles from Earth.
Hayabusa2 on Wednesday captured and transmitted to Earth one of its final images of Ryugu, or Dragon Palace, named after a sea-bottom castle in a Japanese folk tale, as it slowly began moving away from its temporary home, the agency said.
The probe will continue its “farewell filming” of the asteroid for a few more days.
Hayabusa2 will adjust its position around November 18 after retreating 40 miles from the asteroid and out of its the gravitational pull. It will then receive a signal from Jaxa to ignite a main engine in early December en route to the Earth’s vicinity.
The spacecraft made touchdowns on the asteroid twice, despite difficulties caused by Ryugu’s rocky surface, and collected data and samples during its 18-month mission since arriving in June 2018.
In the first touchdown in February, it collected surface dust samples. In July, it collected underground samples for the first time in space history after landing in a crater it had earlier created by blasting the asteroid surface.
Hayabusa2 is expected to return to Earth in late 2020 and drop a capsule containing the precious samples in the Australian desert.
It took the spacecraft three and a half years to arrive at the asteroid, but the journey home is much shorter thanks to the current locations of Ryugu and Earth.
Jaxa scientists believe the underground samples contain valuable data unaffected by space radiation and other environmental factors that could tell more about the origin of the solar system 4.6 billion years ago.
Asteroids, which orbit the sun but are much smaller than planets, are among the oldest objects in the solar system and may help explain how Earth evolved.
Hayabusa2 scientists also said they believe the samples contain carbon and organic matter and hope they could explain how they are related to Earth.