What Are Dust Grains Made of? How to Find Their Chemical Composition

We can infer the chemical nature of dust in space by comparing abundances of elements in stars (which are too hot for dust grains to exist) with elements in the gas of interstellar space. Some elements are apparently missing from the gas in interstellar space, and we may assume that those elements are locked up in dust grains. A more direct way is to collect cosmic dust grains in the Solar System, return them to Earth, and sort them into interplanetary dust grains and true interstellar dust grains. These methods give compositions that suggest that interstellar grains are mainly silicates and carbons.