Asteroids are some of the oldest objects in the Solar System: leftovers from the chaotic time when planets were assembling from dust and rock. They’re time capsules, preserving clues about what the early Solar System was like, and, ultimately, what the building blocks of planets are.
Knowing what an asteroid is made of also matters for very practical reasons. If an asteroid were ever on a collision course with Earth, its composition would affect how dangerous it is, how it breaks up in the atmosphere, and how we might successfully nudge it away. This area of research is called planetary defence.
Understanding the make-up of asteroids also matters for the future of exploration: some asteroids may contain metals, minerals, and even water – potentially useful resources. But how can we tell what asteroids are made of when most of them are millions of kilometres away?
