Abstract

Extraterrestrial materials include meteorites that fall naturally to the Earth, as well as samples such as the Apollo and Luna collections collected in situ and returned to Earth by spacecraft. The samples contain highly detailed records of the conditions, processes, and materials that formed them, and these records can be studied in the laboratory with a wide array of modern analytical techniques. Meteorites are typically hand-sized specimens that are samples of asteroids, small relict planetismals that originally escaped incorporation into planets and contain preserved materials dating back to the earliest history of the solar system. Meteorites are complex assemblages of a variety of components, and among the most exotic of these are interstellar grains that are older than the Sun and planets. Interplanetary dust particles are essentially submillimeter-size meteorites that contain materials from comets as well as asteroids. Like the asteroids, the comets are also planetismals, but they formed beyond Saturn, whereas most of the asteroids formed between Mars and Jupiter.