protolith—the original rocks from which igneous, metamorphic, or sedimentary rocks were formed

pyroclastic—a type of rock material formed by volcanic explosion

pyroxene—a group of common ferromagnesian rock-forming minerals

regolith—on the Moon, the surface rock debris that overlies bedrock

remanent magnetization—also called paleomagnetism, the component of a rock’s magnetism that has a fixed direction and is independent of Earth’s magnetic field

rheology—the study of the deformation and flow of matter

SBE—surface boundary exosphere

SELENE—Selenological and Engineering Explorer, a Japanese Aerospace Exploration Agency lunar orbiter

SIM—the Apollo Scientific Instrument Module, which contained panoramic and mapping cameras, a gamma-ray spectrometer, a laser altimeter, and a mass spectrometer

SIMS—secondary-ion mass spectrometry

SMART-1—Small Missions for Advanced Research in Technology, a European Space Agency lunar mission

SMD—NASA’s Science Mission Directorate

SPA—the lunar South Pole-Aitken Basin

stratigraphy—the study of rock layers

TEM—transmission electron microscopy

U-Pb geochronology—the determination of the age of a rock based on radioactive decay of isotopes of U and Th to Pb, usually in the mineral zircon

VSE—NASA’s Vision for Space Exploration

xenolith—a foreign inclusion in an igneous rock

zircon—a silicate mineral (ZrSiO₄)