When it comes to protecting Earth from impacts, it’s crucial to know what asteroids are made of. NASA is working on a device to find out

The Solar System is filled with small asteroids and comets, all whizzing around in varying orbits. They represent both a threat to our planet – as demonstrated by the Chelyabinsk meteor in 2013 – and an opportunity for in-space mining. But if we are to deflect or exploit these bodies, we need to know what they are made of, and ideally without having to go to the trouble of landing on them all. Fortunately, Dr Gary Hughes of California Polytechnic State University has a solution to this problem, and he has received funding from NASA to work on it.

We can figure out the compositions of stars over tremendous distances because they are hot bodies emitting light, and we can analyse this light with a technique called spectroscopy. If you let sunlight fall on a prism, you’ll see a rainbow split out of the white light, but more careful study will reveal dark lines cutting through the colours at various points. This is because the matter the light is shining through absorbs characteristic wavelengths of light, leading to these gaps – helium was actually found in the Sun this way before it was identified on Earth. But the small objects NASA is interested in interrogating are cold and only reflect light rather than emitting it, so to counter this the agency plans to zap them with a laser.