Meteorites
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Meteorites: Definition and Sources
Meteorites are fragments of extraterrestrial bodies that survive their journey through Earth's atmosphere and land on the surface. Most meteorites originate from the asteroid belt, a region between Mars and Jupiter filled with numerous small planetary bodies and their fragments. A small percentage, about 0.5%, come from Mars or the Moon, while some micrometeorites are derived from comets Okrusch2020Scott2011Rubin2020+1 MORE.
Meteorite Composition and Mineralogy
Meteorites are primarily classified into two broad groups: irons (mainly nickel-iron) and stones (mainly silicates). Stones are further divided into chondrites, which contain rounded grains called chondrules, and non-chondritic stones, which are classified by their mineral content . By 2020, about 470 minerals had been identified in meteorites, reflecting a wide range of processes such as condensation around stars, crystallization from melts, thermal metamorphism, aqueous alteration, and shock metamorphism . Chondrites, the most common type, often preserve minerals from the early solar nebula, such as olivine and enstatite, while differentiated meteorites contain minerals formed by crystallization from magmas .
Origin and Age of Meteorites
The majority of meteorites are impact debris from collisions between asteroids. These collisions produce fragments that can eventually reach Earth. Evidence suggests that iron meteorites come from multiple parent bodies, and pallasites likely originate from the transition zone between the core and mantle of their parent asteroids . The cosmic-ray exposure ages of meteorites indicate that they were produced in a few major collisions rather than a continuous process, with most meteorites coming from asteroids that cross Mars' orbit . Some meteorites contain grains, such as silicon carbide, graphite, and diamond, that formed outside the Solar System before its birth, providing a record of stellar nucleosynthesis .
Meteorites and Planetary Formation
Meteorites are crucial for understanding the early stages of the Solar System's formation and the geological evolution of asteroids, the Moon, and Mars. They offer insights into the processes of planetary growth from protoplanetary disks and help interpret the chemical and physical conditions that shaped our Solar System. Meteorites also serve as a reference point for studying planetary systems beyond our own .
Cataloguing and Classification
Over 60,000 meteorites have been collected and catalogued, with detailed records maintained by institutions such as the British Museum. These catalogues include information on authenticated falls, meteorite craters, and the classification of meteorites based on their mineralogy and structure Ott1993Okrusch2020Rubin2020.
Broader Perspectives
Some perspectives, such as those from astrobiology, suggest that meteorites may carry the building blocks of life, like DNA, to Earth. Other cultural and philosophical views see meteorites as cosmic or even divine objects, reflecting their significance beyond just scientific interest .
Conclusion
Meteorites are invaluable scientific resources that provide direct evidence of the processes that shaped our Solar System and beyond. Their diverse origins, mineralogy, and history make them essential for understanding planetary formation, the evolution of celestial bodies, and even the potential for life's building blocks to travel through space Okrusch2020Scott2011Rubin2020+3 MORE.
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