Hayabusa-2: Japan hopes for historic asteroid landing
Japan's space agency (JAXA) believes it has successfully landed two robotic explorers on the surface of an asteroid, making history.
"We don't have confirmation yet, but we are very, very hopeful," project manager Yuichi Tsuda said.
On Friday, the Hayabusa-2 spacecraft despatched a pair of "rovers" to the 1km-wide space rock known as Ryugu.
Rover 1A and Rover 1B will hop around in Ryugu's low gravity, capturing temperatures and images of the surface.
Hayabusa-2 reached the Ryugu asteroid in June this year after a three-and-a-half-year journey.
Officials hope to confirm a successful landing in a day or two, when the spaceship sends data from the rovers to Earth.
Why does it matter?
While the European Space Agency has previously managed to land on an icy comet, this would be the first spacecraft to successfully place robot rovers on the surface of an asteroid.
Asteroids are essentially leftover building materials from the formation of the Solar System 4.6 billion years ago.
Ryugu is a particularly primitive variety, and studying it could shed light on the origin and evolution of our own planet.
The diamond-shaped asteroid has a blackish-coloured surface, and rotates on its axis around once every 7.5 hours.
How did the rovers reach the asteroid?
Early on Thursday morning (GMT), Hayabusa-2 began descending towards the surface of Ryugu, preparing to eject its rovers.
The little hoppers are stored in a drum-shaped container at the base of the "mothership". Collectively, they form a 3.3kg science package known as Minerva II-1.
About 60m (196ft) from the asteroid, Hayabusa-2 initiated the release of the two robots.
Japanese space agency officials said that when the front of the drum is jettisoned into space, the two rovers are ejected from the container and fall independently to the asteroid's surface.
One of the principal concerns for deployment was Ryugu's rougher-than-expected surface, which is carpeted with boulders and has very few smooth patches.
What will they do there?
The 1kg rovers are equipped with wide-angle and stereo cameras to send back pictures from Ryugu. Spine-like projections from the edges of the hoppers are sensors that will measure surface temperatures on the asteroid.
They can hop and float around thanks to a motor-powered internal rotor, which propels the robot across the surface.
They will send back their data to the mothership, which will then relay the information to Earth.
"I am looking forward to seeing pictures. I want to see images of space as seen from the surface of the asteroid," JAXA project manager Yuichi Tsuda said.
When will they get samples?
On 3 October, the mothership will deploy a lander called Mascot, which has been developed by the German Aerospace Center (DLR) together with the French Space Agency (CNES).
And in late October, Hayabusa-2 will descend to the surface of Ryugu to collect a sample of rock and soil.
Further on in the mission, Japan's space agency plans to detonate an explosive charge that will punch a crater into the surface of Ryugu.
Hayabusa-2 would then descend into the crater to collect fresh rocks that have not been altered by aeons of exposure to the environment of space.
These samples will be sent to Earth for laboratory studies.
The spacecraft will leave Ryugu in December 2019 with the intention of returning to Earth with the asteroid samples in 2020.