chondrules

Chondrules are small, typically 0.1 to 2 millimeters in diameter, spherical silicate grains found in chondritic meteorites. They are among the most common constituents of chondrites and are usually embedded in a fine-grained matrix.

Most chondrules are composed primarily of olivine and pyroxene, with minor amounts of glass, metal, and sulfides. Textures include porphyritic, barred-olivine, and radial; such textures record rapid cooling of molten droplets in the early solar nebula. Some chondrules preserve relict grains, revealing precursor materials.

Formation and age: Chondrules are believed to have formed as molten or partially molten droplets in the solar nebula during the first few million years of the solar system. They predate certain other primordial components, and isotopic dating places their formation within the early solar system timeframe.

Formation mechanisms: The heating events that produced chondrules are a subject of ongoing research. Proposed mechanisms include shock waves in the protoplanetary disk, nebular lightning, and high-velocity collisions between planetesimals. It is possible that multiple processes operated in different environments.

Significance: Chondrules provide important constraints on conditions in the solar nebula, including thermal histories and timescales of planet formation. Isotopic dating of chondrules contributes to models of solar system chronology and meteorite formation; together with their frequent occurrence in chondrites, they serve as a key window into the earliest solid materials in our solar system.