TOKYO - Japan will delay the touchdown of its Hayabusa2 spacecraft on the Ryugu asteroid by at least three months owing to its "surprisingly rocky surface", its space agency has said.
Initially scheduled for the end of October 2018, the landing is now set for late January 2019 at the earliest.
Even so, the probe has already amassed valuable data since it approached the asteroid in June. In what was a world first, it also succeeded in deploying onto the asteroid surface three moving autonomous observation robots that have transmitted data to scientists on Earth.
All eyes in the space community are on the six-year odyssey of the Hayabusa2 probe, which was launched from Japan in December 2014 and is due to return to Earth with samples of asteroid matter by end-2020.
The Japan Aerospace Exploration Agency (Jaxa) hopes the samples will give an insight into the origins and evolution of the solar system. The current probe follows Jaxa's first asteroid explorer, Hayabusa, which returned to Earth in 2010. "Hayabusa" means falcon in Japanese.
Hayabusa2 project manager Yuichi Tsuda said on Friday (Oct 12) the postponement of the touchdown was due to the difficulties in finding a smooth landing site.
The surfaces of asteroid Ryugu, which means Dragon Palace in Japanese, are rougher and rockier than initially expected, Dr Tsuda added.
Three landing sites - each with an area of 100m by 100m - had been identified earlier. But he explained that better imaging of the asteroid surface showed the sites were littered with boulders and rocks, and this required his team to be more precise in landing the spacecraft.
Two landing rehearsals will be held in October, when Hayabusa2 will descend to an altitude of 25m above the asteroid surface. The probe, which arrived at Ryugu in late June, is now programmed to keep a distance of 20km from the asteroid.
Jaxa will momentarily lose contact with the probe for the next two months as the asteroid will be on the other side of the sun from Earth. Ryugu, which is shaped like a spinning top, has a diameter of about 880m and orbits the Sun once every 16 months, passing near the orbits of Earth and Mars.
On Sept 21, a pair of Minerva-II1 micro-rovers were dropped from Hayabusa2 onto the asteroid. The robots are loaded with cameras and sensors and, making use of Ryugu's low gravity, bounce around the asteroid's surface to survey its physical features.
On Oct 3, a 10kg observation robot known as Mascot, or Mobile Asteroid Surface Scout, was deployed onto the Ryugu surface. It had a battery span of 17 hours, during which it gauged surface temperatures, took images at multiple wavelengths, and investigated materials.
"Our primary mission is to gain more knowledge about Ryugu itself as information after the formation of the solar system has been conserved on the asteroid. And unlike larger planets, there has been no space weathering or erosion," Dr Tsuda said.
He identified several reasons the Hayabusa2 mission is significant.
Not only can the probe unlock scientific discoveries, it can also represent the future of space exploration engineering, given the unprecedented success landing of moving autonomous robots on an asteroid surface.
Dr Tsuda also hoped to find answers that can bolster Earth's defence.
"There are a number of asteroids that are close to the Earth's orbit and there is a certain degree of probability of collision with Earth, and so there has been rising attention to protect the Earth from such cases."
There is also the potential discovery of resources in outer space that can be mined for use on Earth, he added, noting an emerging trend of start-ups across the world looking at doing so.