As you might imagine, the choices here are caricatured so that the science lab crew can focus on the pilotís three choices. Simplifications include:
Mineral surfaces may each have numerous characteristic spacings. We simplify matters here by considering only one of the larger spacings that a given mineral would present, not all spacings.
Interplanetary dust, and we expect cometary debris, contains many silicates (silicon oxide minerals which are not dominant phases in either solid fuel rocket exhaust or in metallic meteorities). However, the elemental silicon structure considered in this scenario is not among them!
Once the source of the debris is identified, mission choices will in general not be so clear cut. In this case we assume that Mission Control has additional information which translates these identifications into the well-defined pilot choices listed above.