A Japanese probe has reached an asteroid 300 million kilometres away to collect information about the birth of the solar system and the origin of life after a more than three-year voyage through deep space.
The probe settled into an observation position 20 kilometres above the Ryugu asteroid, officials from the Japan Space Exploration Agency (JAXA) said on Wednesday.
"We have confirmed the arrival of Hayabusa2 at the Ryugu asteroid," JAXA said in a statement.
Ryugu is thought to contain relatively large amounts of organic matter and water, the stuff of life, and scientists hope samples taken from the asteroid will offer clues about what gave rise to life on Earth.
JAXA's announcement came just days before the UN's International Asteroid Day on 30 June, a global event to raise awareness about the hazards of an asteroid impact and technological progress to counter such a threat.
Photos of Ryugu — which means "Dragon Palace" in Japanese, a castle at the bottom of the ocean in an ancient Japanese tale — show an asteroid shaped a bit like a spinning top with a rough surface.
The probe will land on Ryugu in coming months and take samples "to clarify the origin of life," JAXA said in an earlier statement.
Hayabusa2, about the size of a large fridge, is equipped with solar panels and is the successor to JAXA's first asteroid explorer, Hayabusa — Japanese for falcon.
That probe returned from a smaller, potato-shaped, asteroid in 2010 with dust samples despite various setbacks during its epic seven-year Odyssey and was hailed as a scientific triumph.
The Hayabusa2 mission costs 30 billion yen ($274 million) and the probe was launched in December 2014. It will stay with the asteroid for 18 months before heading back to Earth with its samples in late 2020.
To collect its samples, it will release an "impactor" that will explode above the asteroid, shooting a two-kilogram (four-pound) copper object into the surface to create a crater a few metres in diameter.
From this crater, the probe will collect "fresh" materials unexposed to millennia of wind and radiation, hoping for answers to some fundamental questions about life and the universe, including whether elements from space helped give rise to life on Earth.
The probe will observe the surface with its camera and sensing equipment but will also drop tiny MINERVA-II rover robots as well as a French-German landing package named Mobile Asteroid Surface Scout (MASCOT) for surface observation.