After a journey of three and a half years, the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa 2 spacecraft is sidling up to its destination, a small asteroid called Ryugu. The probe is now only around 45 kilometres away, slowing down to enter orbit and begin its survey of the asteroid .

The approach is a tricky one, says JAXA’s Elizabeth Tasker. “A tiny mistake can mean you miss the target entirely,” she says. “The distances are equivalent to trying to hit a 6 centimetre target in Brazil from Japan.”

Assuming …