Allende meteorite

Allende meteorite. The Allende meteorite is one of the most significant and extensively studied meteorites in history. It fell over the Mexican state of Chihuahua in early 1969, scattering thousands of fragments across a wide area. As a CV3 carbonaceous chondrite, it contains some of the oldest and most primitive materials in the Solar System, providing an invaluable window into its formation and early evolution.

Description and composition

The meteorite is characterized by a dark fusion crust surrounding a lighter, friable interior rich in chondrules and calcium-aluminium-rich inclusions. Its matrix contains a complex assemblage of minerals, including olivine, pyroxene, and feldspar, alongside refractory phases like spinel and hibonite. A key feature is the presence of abundant, millimeter-sized CAIs, which are among the oldest known solid materials formed in the Solar System. These inclusions often contain exotic minerals such as perovskite and melilite, and the meteorite also contains presolar grains of diamond and silicon carbide that predate the Sun.

History and fall

The fall occurred at approximately 01:05 local time on February 8, 1969, creating a spectacular fireball witnessed over a vast region of northern Mexico and the southwestern United States. The event was recorded by the U.S. Air Force and numerous civilian observers, with sonic booms heard across the Chihuahuan Desert. The meteoroid fragmented violently in the Earth's atmosphere, producing a massive strewn field extending over hundreds of square kilometers near the village of Pueblito de Allende. Local residents and scientists from institutions like the University of Mexico began recovering fragments within days, with the total collected mass estimated at over two metric tons.

Scientific significance

Its arrival just months before the Apollo 11 mission provided planetary scientists with pristine, ancient material for comparative study against lunar samples. Research on its components has fundamentally shaped our understanding of nucleosynthesis, solar nebula processes, and early planetary differentiation. Studies of its isotopic anomalies, particularly in elements like oxygen, magnesium, and calcium, have revealed distinct stellar sources for Solar System material. The discovery of the short-lived radionuclide aluminium-26 within its CAIs provided critical evidence for the injection of fresh supernova material into the nascent Solar System.

Classification and origin

It is classified as a CV3 carbonaceous chondrite, specifically of the oxidized CV subgroup, linking it to the Vigarano meteorite type. This classification indicates it experienced minimal aqueous alteration or thermal metamorphism on its parent body, preserving its primitive state. While its exact parent body remains unidentified, spectral studies suggest a probable link to C-type asteroids, such as those found in the outer asteroid belt. The orbital elements calculated from its fall trajectory are consistent with an origin from the main belt, possibly from a body like asteroid 221 Eos.

Specimen distribution and curation

Major institutions worldwide hold significant collections, including the Smithsonian Institution, the Field Museum of Natural History, and the University of California, Los Angeles. The NASA Johnson Space Center and the Meteoritical Society database curate samples for international research. Specimens are also held at the University of Chicago, the Max Planck Institute for Chemistry, and the National Museum of Natural History, France. These collections are vital for ongoing research in cosmochemistry and planetary science, with samples allocated through bodies like the NASA Astromaterials Acquisition and Curation Office.

Category:Meteorites found in Mexico Category:Carbonaceous chondrites Category:1969 in science