Japan’s Hayabusa 2 spacecraft has deployed two target markers around asteroid Ryugu. The deployment took place at 5.17pm BST on 17 September from an altitude of 1km. In the minuscule gravity of the asteroid, the unpowered markers are still falling to its surface. They are expected to land sometime over the weekend or early next week at the latest.

The 10cm-wide markers are covered in a highly reflective material that makes them easy to observe from the main spacecraft, which has now risen to a height of 20km (12.4 miles). By tracking their descent, planetary scientists can deduce the precise gravitational field that the asteroid generates, which reveals its internal structure. Hayabusa 2 arrived at Ryugu on 27 June 2018. It has already released three small rovers to the surface and performed two touchdowns to collect surface material.

Following the deployment of its final onboard lander, which is scheduled for October, the spacecraft will leave the asteroid and begin its return to Earth. Due to arrive in December 2020, Hayabusa 2 will release a capsule containing the asteroid samples it has collected. This capsule will re-enter Earth’s atmosphere and use parachutes to land in Australia.