Have you noticed the black cylinder extending from the front end of the asteroid explorer Hayabusa2? That’s its “sample horn,” a mechanism for collecting rock and sand samples from the surface of the asteroid Ryugu. And it’s a very ingenious device indeed. It took it only seconds to secure a sample, no matter what surprises the asteroid held.
The sampler horn system was developed by NEC, while the actual mechanism was designed and manufactured by Sumitomo Heavy Industries, Ltd. It takes a pragmatic approach unaffected by the nature of the asteroid’s surface. When the explorer lands on an asteroid and the tip of the sampler horn touches the surface, a signal is sent to the spacecraft telling it that it has touched down. The projector inside then shoots a spherical projectile made of rare metal, which breaks the surface and sends fragments flying. The resulting cloud of debris ends up in the catcher.
Most people probably imagine that sand is collected from an asteroid by scooping it up with a shovel. To use a shovel, though, you need a surface covered in sand; and because asteroids have such a weak gravitational field, the spacecraft could end up rising off the ground, shovel and all. Plus using a shovel is a complicated operation. The spacecraft has to touch down on the surface with its “legs” and then scoop up sand with the equivalent of its “hands”. For those reasons NASA’s asteroid explorer OSIRIS-REx, for example, took a different tack. It collected asteroid samples by releasing a burst of nitrogen gas from the end of its sampling arm and capturing the sand stirred up as a result. But that approach, too, assumes that the asteroid is sandy. In short, a shovel is not the preferred option when you won’t know whether the asteroid’s surface is covered in fine sand or big boulders until the probe actually gets there.