Published online by Cambridge University Press: 11 August 2021
Meteorites are delivered to Earth from at least 100 different asteroids as well as from the Moon and Mars. A significant fraction of micrometeorites and interplanetary dust particles are from comets. Some of the meteorite parent bodies melted and differentiated; they developed metal cores and basaltic crusts. Other bodies never melted, preserving materials formed in the solar nebula. Some unmelted asteroids were thermally metamorphosed; many were aqueously altered. Meteorites suffered shock damage on their parent bodies, ranging from fracturing and brecciation to impact melting and devolatilization. After their formation, many samples experienced thermal metamorphism, aqueous alteration, and shock metamorphism to different extents; some were altered and/or shocked more than once.