Extraterrestrial Materials

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.

Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

“…Challenger expedition to the central Pacific. They assigned a cosmic origin to their magnetically extracted round particles, an interpretation which is still accepted [e.g., Brownlee, 1981]. Because such extraterrestrial spherules are typically very pure iron oxides with an Al/Mg ratio (1 and have a few percent of Ni [e.g., Brownlow et al, 1966], we can exclude this possibility for our samples.…”

Micrometeorites from the northern ice cap of the Novaya Zemlya archipelago, Russia: The first occurrence

“…Olinger et al 1990). While this data does not exist for the Novaya Zemlya spherules, more general criteria for identifying cosmic spherules (CS) (Blanchard et al 1980;Brownlee 1981) and a similarity between the Novaya Zemlya spherules and CS with a proven extraterrestrial origin (Papanastassiou, Wasserburg, andYiou, Raisbeck, and Brownlee 1985;Raisbeck et al 1986;Nishiizumi et al 1992) suggest they are extraterrestrial. The textures, mineralogy, and chemistry of Fig.…”

“…Initially, deep-sea deposits (red clay) were the main source for cosmic spherules (Brownlee 1981(Brownlee , 1985, but now micrometeorites are collected mainly from polar ice in the ablation zone of the Greenland ice cap (Maurette et al 1986 and the Antarctic ice sheet (Maurette et al 1991(Maurette et al , 1992Taylor, Lever, and Harvey 2000;Taylor, Lever, and Govoni 2001;Iwata and Imae 2001). Other polar ice caps can provide specific areas for micrometeorite sampling, too.…”