Asteroids are tiny planets, metres to kilometres across, that orbit between Mars and Jupiter (though some come close to Earth). They’re the leftover bits from the origin of the solar system, threats to life on Earth if they hit us, and possible sources of minerals – and water – that will fuel a space-based economy in 50 or 100 years’ time.

The ones with water are especially interesting. Though previous space missions have visited dry rocky asteroids, it’s only this year we’ve seen close up the dark bodies with water-bearing minerals.

Nasa launched the Osiris-Rex mission to asteroid 101955 Bennu in 2016. It arrived in December 2018, and has spent its time since then looking for a good place to touch the surface and grab a sample to bring back to Earth. It turns out finding such a spot was a lot harder than expected.