Elements Covers

Posts by Donald E. Brownlee

Flyby Missions to Comets and Return Sample Analysis

Images from flyby missions show comets to be geomorphically diverse bodies that spew jets of gas, dust, and rocks into space. Comet surfaces differ from other small bodies because of their ejection of mass into space. Comet solids >2 µm are similar to primitive meteorite ingredients and include the highest temperature materials made in the early solar system. The presence of these materials in ice-rich comets is strong evidence for large-scale migration of solid grains in the early solar system. Cometary silicates appear to have formed in numerous hot solar system regions. Preserved interstellar grains are rare, unless they have eluded identification by having solar isotopic compositions

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Cosmic Dust: Building Blocks of Planets Falling from the Sky

Throughout its history, Earth has accreted microscopic dust falling from space. Decelerating from cosmic speeds at the top of the atmosphere, the smallest particles can take weeks to reach the ground, failing a rate of 1 m−2 day−1. Although usually hidden among terrestrial materials, extraterrestrial particles can be collected from select environments and positively identified by their unique properties. Unmelted cosmic dust is often composed of large numbers of smaller silicate, sulfide, and organic components—the preserved materials from the early Solar System. Cosmic dust particles are samples of comets and asteroids and they are important samples of the initial materials that were to build the solid planets.

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