What is the Allende meteorite?
Allende is a large carbonaceous chondrite that fell in Mexico on 8 February 1969, providing tonnes of material rich in CAIs, the oldest solids in the Solar System.
In the early hours of 8 February 1969, a brilliant fireball lit up the sky over Chihuahua in northern Mexico. It broke apart and scattered thousands of stones over a large area near the village of Pueblito de Allende.
A huge fall. More than 2 tonnes of stones were collected, and estimates of the total fallen mass are higher. Allende is the largest known carbonaceous chondrite fall. Stones were collected by local people and by scientists from around the world, who hurried to the area.
What it is. Allende is a CV3 carbonaceous chondrite. It is dark grey, with abundant chondrules and many white or pinkish calcium-aluminium-rich inclusions (CAIs), some centimetres across.
Scientific importance. The sheer quantity of Allende material, available just as laboratories were gearing up for the Apollo Moon samples, made it one of the most studied meteorites in history. - Its CAIs were used to establish the age of the Solar System, about 4,567 million years. - Studies of Allende found evidence of short-lived radioactive aluminium-26, showing it was present in the early Solar System. - Oxygen isotope studies of Allende minerals in 1973 revealed unexpected variations, launching a major field of research. - New minerals have been discovered in Allende, some named after scientists.
Availability. Because so much fell, Allende specimens are relatively easy for collectors to obtain, often as fragments showing chondrules and CAIs.
Allende is a classic example of how a single fall can transform scientific understanding.