Final answer:
MASCS stands for Mercury Atmospheric and Surface Composition Spectrometer, an instrument on the MESSENGER spacecraft for studying Mercury's atmosphere and surface.
Step-by-step explanation:
Within the context of the Mercury Atmospheric and Surface Composition Spectrometer, MASCS stands for Mercury Atmospheric and Surface Composition Spectrometer. This instrument was part of the payload of the MESSENGER spacecraft, which orbited Mercury. The MASCS was designed to study both the atmosphere and surface of Mercury, providing essential data to help understand the planet's composition and its geologic and atmospheric processes.