Bennu's surprise
When a spacecraft touched the asteroid Bennu, the surface acted more like a ball pit than solid ground.
Bennu is a small asteroid, about half a kilometre across. It is dark, and covered in boulders.
In 2020 an American spacecraft called OSIRIS-REx reached out its long arm and touched Bennu's surface. It puffed out gas to stir up the pebbles, and caught some in a collector.
Scientists had a surprise. The arm sank into the surface easily. Bennu's surface is a loose pile of rocks, held together only gently by gravity. Pushing into it was a bit like pushing into a ball pit.
The spacecraft caught so much material that the lid could not close properly at first. Some pebbles floated away before it was sealed.
In September 2023 the sample capsule landed in the desert in Utah, in the United States. It held about 120 grams of Bennu.
Inside, scientists have found building blocks of life, such as amino acids, along with salts left behind by water that dried up long ago.
Bennu's name was chosen by a schoolboy, Michael Puzio, in a naming competition in 2013.